key: cord-0770252-5x1cqkk1
authors: Coughlan, Lynda; Kremer, Eric J.; Shayakhmetov, Dmitry M.
title: Adenovirus-based vaccines – a platform for pandemic preparedness against emerging viral pathogens
date: 2022-01-31
journal: Mol Ther
DOI: 10.1016/j.ymthe.2022.01.034
sha: 7c21a8c70c6ab8dbdb96d257fe624368a67c0728
doc_id: 770252
cord_uid: 5x1cqkk1

Zoonotic viruses continually pose a pandemic threat. Infection of humans with viruses for which we typically have little or no prior immunity, can result in epidemics with high morbidity and mortality. These epidemics can have public health and economic impact, and can exacerbate civil unrest or political instability. Changes in human behavior in the past few decades: increased global travel, farming intensification, the exotic animal trade, as well as the impact of global warming on animal migratory patterns, habitats and ecosystems, contribute to the increased frequency of cross-species transmission events. Investing in the pre-clinical advancement of vaccine candidates against diverse emerging viral threats is crucial for pandemic preparedness. Replication-defective adenoviral (Ad) vectors have demonstrated their utility as an outbreak-responsive vaccine platform during the SARS-CoV-2 pandemic. Ad vectors are easy to engineer, are amenable to rapid, inexpensive manufacturing, are relatively safe and immunogenic in humans, and importantly, and do not require specialized cold-chain storage, making them an ideal platform for equitable global distribution, or stockpiling. In this review, we discuss the progress in applying Ad-based vaccines against emerging viruses, and summarize their global safety profile, as reflected by their widespread geographic use during the SARS-CoV-2 pandemic.

The ongoing threat posed by emerging viruses has been highlighted following the introduction of a novel 1 recent years, and this class of Ab can also contribute to viral clearance. For example, Abs can agglutinate 47 viral particles (v.p), which make these large aggregates an easy target for immune cells to phagocytose 48 the complex via Fc receptors (FcRs) and degrade the virus. Alternatively, non-neutralizing Abs can also 49 bind to viral glycoproteins expressed on the surface of infected cells, and target those cells for destruction 50 via Fc-mediated antibody dependent cellular cytotoxicity (ADCC) 3-6 , or phagocytosis (ADCP) 7 . Abs can 51 also activate the complement pathway, which opsonizes and promotes the phagocytosis of viruses and/or 52 damages the envelope (phospholipid bilayer) present on some viruses. 53

In non-professional APCs, antigen presentation is thought to be limited to MHC II presentation and 54 preferentially induces a Th2-skewed response. However, in professional APCs (e.g. dendritic cells 55 (DCs), Langerhans cells, macrophages) a phenomenon called cross-presentation occurs, where proteins 56 that are taken up from the extracellular environment can be loaded onto MHC I molecules to promote a 57 Th1 response. There are several pathways toward cross-presentation in APCs, including cytosolic and 58 vacuolar. Following uptake of exogenous antigen by macropinocytosis or phagocytosis, antigen escape 59 from the early endosome, or fusion of the endosome with the endoplasmic reticulum (ER), and 60 subsequent degradation of antigen by the proteasome, facilitates peptide loading onto recycled cell 61 surface MHC class I molecules. It is worth noting that cross-presentation can operate independently of 62 Nucleic acid-based vaccines: DNA and mRNA. A primary difference within nucleic acid-based 143 vaccines, as compared with inactivated, protein or nanoparticle-based platforms, is that the antigen is 144 produced from the cell that takes up the vaccine following immunization. Transgene expression of the 145 target antigen from mRNA likely persists for a few days 41 , while DNA vector-based vaccines may provide 146 more sustained antigen presentation 9,42 . Antigens encoded by nucleic-acid vaccines can also be targeted 147 to the cell surface to allow more efficient detection by the developing immune response (Fig. 2) . DNA-148 based vaccines (plasmids), which have been explored for greater than 3 decades, are rapidly designed, 149 easily produced, scalable, and thermostable. Clever approaches have also allowed the production of 150 plasmids void of antibiotic resistance genes 43 . DNA-based vaccines also preferentially induce a Th1-151 biased immune response. Avoiding degradation prior to reaching the nucleus can be a limiting factor for 152 DNA-based vaccines. However, to date, these vaccines have been encouraging in preclinical studies, 153 and significant success in human clinical trials may not be far off [44] [45] [46] . Innate responses to DNA and RNA 154

include PRRs that detect uncapped mRNA (TLR7) and unmethylated CpG (TLR9), and those that detect 155 antimicrobial peptides (AMP)/coagulation factors linked to viral capsid (TLR4) [47] [48] [49] . 156

As with plasmid-based vaccines, RNA vaccines have been explored for 3 decades too. The breakthrough 157 that made mRNA viable as a vaccine platform is the modification of their bases, which prevents excessive 158 immunostimulation, allowing evasion of PRR recognition, preventing premature degradation, and 159 therefore enabling increased and sustained transgene antigen expression 50 . In addition, advances in 160 formulation chemistry facilitated the encapsulation of modified mRNA in lipid nanoparticles (LNPs), which 161 display biocompatibility and can accommodate a large mRNA payload 50 , with the capacity to encode 162 more than one antigen for a multi-valent vaccine 51 . Following uptake in target cells at the site of injection, 163 mRNA-based vaccines do not have to enter the nucleus. Therefore, a significant trafficking hurdle is 164 avoided, and mRNA can be very rapidly translated into the targeted protein/antigen in the cytoplasm. The 165 subject of applying mRNA vaccines against infectious diseases is beyond the scope of this review, and 166 is covered in detail in comprehensive reviews elsewhere 22, 50 . 167 J o u r n a l P r e -p r o o f Pseudotyped, replication-defective and replication-competent viral vectors. The concept of using 168 viral vectors to deliver gene expression cassettes encoding targeted antigens is also greater than 3 169 decades old. Of note, some of the first HAdV type 2 and 5 vectors were "vaccines" 52 (i.e., Ad, MVA, AAV) which is then expressed in cells that take up the vaccine (Fig. 2) . Typically, vectors 179 are injected intramuscularly (i.m). Advantages include robust and inexpensive production, high safety 180 profiles, and a tendency to generate Th1-skewed, or balanced Th1/Th2 responses. Drawbacks include 181 pre-existing immunity against the vector, which can reduce vaccine efficacy and may preferentially 182 amplify a pre-existing response (versus generate a robust de novo response against the encoded 183 transgene(s)). Alternatively, viral vectors can be pseudotyped/genetically engineered to display 184 heterologous glycoprotein antigens (i.e., VSV, NDV), vectors can be (re-)targeted to specific cell types 185 via modification of the receptor-binding domains, or (sero)types with a preferential tropism (e.g., APCs) 186 can be selected. Moreover, some vectors can be engineered for a single replication cycle to boost 187 efficacy 67 , or capsid proteins can be modified to include antigenic epitopes from a target pathogen 68, 69 . 188

The latter approach allows antigen to be processed and presented by MHC II during vaccine uptake, and 189 depending on the platform, simultaneous production of genome-encoded antigen can allow for MHC I 190 presentation. 191 Specifically, replication-defective Ad vaccines have several characteristics that enhance their potential 192 as an adaptable plug-and-play platform technology, well-suited to pandemic preparedness initiatives 70 . 193 They have a stable dsDNA genome which can be engineered to encode one or more vaccine 194 antigens 58,71-73 , their broad geographic use during the SARS-CoV-2 pandemic highlights their suitability 195 for rapid manufacturing to meet global demand, they are safe and immunogenic in healthy adults 54,56,74-196 77 , infants as young as 1 week of age 78,79 , the elderly 54 , and immunocompromised 80-82 , and they are 197 compatible with thermostabilization and lyophilization procedures [83] [84] [85] , allowing them to be stockpiled or 198 distributed without the need for specialized ultra-cold storage. Finally, they are substantially cheaper than 199 mRNA platforms, potentially allowing for a more equitable global vaccine distribution. These factors are 200 all important considerations when developing vaccines against outbreak pathogens, which may be 201 geographically endemic in low-and-middle-income-countries (LMICs). 202

Beyond vaccines for SARS-CoV-2, which are outlined in detail in a recent review 86 

Marburg virus (MARV) was identified as the causative agent for Marburg virus disease (MVD) following 218 vaccines encoding the EBOV GP, or nucleoprotein (NP) at doses of 1 x 10 10 (v.p) in mice or 2 x 10 12 v.p 240 in NHPs, in a single shot versus homologous prime:boost regimen administered i.m 101,104 . As reported for 241

Ad-based vaccines 105 , induction of antigen-specific immune responses was rapid (<3 weeks). However, 242

Ab responses to GP were not boosted by the 2 nd homologous Ad5-GP immunization, likely due to anti-243 vector immunity. When a single-shot regimen containing an equal mixture of Ad5-GP/Ad5-NP was tested 244

in NHPs, it conferred complete protection from infection within one month of immunization 104 , even with 245 a high challenge dose. Building upon these promising findings, the Nabel laboratory subsequently 246 evaluated strategies to modify the encoded GP antigen, to eliminate its inherent cytopathic effects, while 247 maintaining protective efficacy, or used approaches to improve GP-specific immune responses by 248 enhancing transgene expression by codon optimization 106, 107 . 249

Considering the more advanced pre-clinical state of Ad-based vaccines against Ebola virus relative to 250 other outbreak pathogens, a broader range of studies exist. These include testing mucosal delivery, the 251 use of diverse human and non-human Ad vector platforms, heterologous prime:boost regimens, or the 252 construction of multi-valent vaccine candidates. Ad5 vaccines encoding GP from Zaire ebolavirus, 253 administered intranasally (i.n) to several animal species (i.e., mice, guinea pigs, NHPs) have been shown 254 to provide complete protection from lethal challenge, comparable to i.m immunization 108-111 , and can 255 bypass pre-existing immunity to the Ad5 vector carrier 108,110 . Alternative strategies to overcome pre-256 existing immunity to common Ad serotypes include the use of Ad vectors derived from rare, or non-human 257 Ads 9,13,112 . Yang and colleagues reported the construction of two chimpanzee Ad vectors, AdC7 and 258

AdC68 expressing the Ebola virus GP from the 2014 outbreak. A single i.m immunization with each vector 259

at 2 x 10 10 v.p elicited GP-specific Ab responses, although only AdC68 elicited detectable antigen-specific 260 IFN-γ ELISpot responses 113 . This observation again emphasizes that distinct Ad platforms elicit a range 261 of immunological phenotypes 9 , and vaccines will thereby require customization for specific disease 262 targets. When tested in a heterologous prime:boost regimen, AdC7-AdC68 was found to be optimal, 263 inducing GP-binding Abs, pseudovirus NAbs and GP-specific T-cells. ChAd3 and ChAd63-based 264 J o u r n a l P r e -p r o o f vaccines have also been tested in NHPs, with the ChAd3 platform being identified as superior in eliciting 265 protection from lethal challenge, a factor associated with a higher magnitude of both cellular and humoral 266 immune responses 102 . However, protective immunity waned 10 months post-immunization with a single-267 shot of ChAd3, which may limit its use beyond emergency, reactive-use applications. However, this effect 268 could be overcome by use of a heterologous MVA boost at week 8, which facilitated the maintenance of 269 a high frequency of TNF and IFN-γ + co-producing CD8 + T-cells at the 10-month challenge timepoint, 270 which were associated with increased protection. The ChAd3 platform, as well as its use in a 271 heterologous prime:boost regimen with MVA 55 , has now been evaluated in human clinical trials and has 272 been found to be safe and immunogenic in children 88 and healthy adults 89,92 ( antigen design facilitated encoding of conserved T-cell epitopes, or "pan-filovirus epitopes", from 289 nucleoprotein (NP), matrix (M) and polymerase (L) in ChAdOx1, or MVA vectors 116 (Fig. 3A) . In this 290 approach, the GP was not included as an antigen, and no filovirus-specific NAbs were induced. Despite 291 this, a heterologous Ad prime:MVA boost conferred complete protection from challenge with EBOV and 292 MARV in mice, demonstrating the breadth of protection which can be elicited towards highly conserved 293 T-cell epitopes. 294

Lassa virus (LASV) is an enveloped single-stranded, bisegmented, ambisense RNA virus which is a 295 member of the order Bunyavirales (Fig. 3B) . The virus was first identified in Nigeria in 1969 as the 296 causative agent of an acute viral hemorrhagic fever. Infection is caused by exposure to the urine or feces 297 of infected Mastomys rats, and LASV infects 100,000-500,000 people annually 95 . Infection can be 298 asymptomatic-mild in endemic areas, and as such the true incidence is unclear. However, high mortality 299 can be observed in hospitalized patients (15-70%) and during the third trimester of pregnancy, where of 300 fetal loss is common and mortality can reach 90% 117 (TABLE. 1). Long-term health effects in survivors 301 are common, including chronic neurological complications and hearing loss. As a result of its high case 302 fatality rate, documented reports of human-to-human transmission, the potential to cause nosocomial 303 infections, as well as a history of imported cases in countries outside of West Africa, the development of 304 an effective vaccine suitable for use in high-risk populations is a priority for global health security. 305 A correlate of protection for Lassa fever has not been conclusively identified. A role for cellular immunity 306 in protection has been inferred from pre-clinical models and human survivors, where the development of 307

NAbs has been found to be delayed or weak 95 . In contrast, T-cell activation has been associated with 308 control of infection in NHPs 118 . Ad-based vaccines are well-established to elicit potent cellular immune 309 responses, suggesting they may be a suitable platform for protecting against Lassa fever. To date, immunization. Serum Abs capable of binding both NP and GP were detected in vaccinated animals, but 317

NAbs prior to challenge were low (PRNT50: 1:10), and were only observed in 3/8 animals. Despite this, 318

all Ad-immunized animals completely survived the challenge and LASV was not detected in the brain, 319 lung, liver, spleen, kidney or serum, whereas animals immunized with a control Ad succumbed to disease. 320

The authors hypothesized that non-neutralizing anti-NP or anti-GPC Abs capable of engaging Fc-321 mediated effector functions might contribute to protection, as this mechanism was proposed as a novel 322 correlate of protection in another study 5 . However, the latter role was not formally investigated in the 323

Maruyama study, nor were antigen-specific T-cell responses. 324 A more recent study described the construction of a ChAdOx1 vaccine against Lassa fever 120 . Again, the 325 LASV GPC antigen was selected, and immunogenicity was evaluated in a single-shot or homologous 326 prime:boost regimen in mice, followed by efficacy testing in Hartley guinea pigs using 1 x 10 5 TCID50 of 327 a guinea pig adapted Josiah strain LASV challenge virus. Mice were immunized i.m with 1x 10 8 IU, and 328 when a boost was administered, the same dose was used with a 28-day interval (D28). T-cell responses 329 to both the encoded lineage IV GPC (Josiah strain), as well as cross-reactive responses towards three 330 heterologous strains from lineage I-III, were measured by ELISpot and flow cytometry, with predominantly 331 CD8 + >CD4 + responses detected. Similarly, immunization with ChAdOx1-GPC resulted in breadth of 332 reactivity against lineage I-III glycoproteins (GP) by ELISA. Interestingly, no benefit of homologous 333 boosting was observed in mice, with comparable levels of T-cells or Abs following the single-shot, or 334 prime:boost regimen. In contrast, an increase in GP-specific Abs was detected in guinea pigs that 335 received the homologous prime:boost. In support of prior evidence which suggested that NAbs are not 336 required for protection against Lassa fever, the ChAdOx-GPC vaccine did not elicit NAb responses, but 337 guinea pigs were 100% protected from clinical disease. Although complete sterilizing protection was not 338 achieved, only very low levels of LASV RNA was detected in the tissues of vaccinated animals. 339

The WHO TTP for a vaccine against Lassa virus prioritizes non-emergency preventative use, which could 340 be used in endemic regions and would be suitable for use in healthcare workers and pregnant people. 

Crimean-Congo hemorrhagic fever (CCHF) is an acute viral infection caused by CCHF orthonairovirus 355 (CCHFV), and transmitted by Ixodid ticks, primarily of the Hyalomma genus. The virus belongs to the 356 order Bunyavirales and is enveloped, with a tri-segmented, negative sense RNA viral genome (Fig. 3C) . 357

There is growing concern regarding increasing reports of imported cases, expanding endemic regions 358 and broadening geographic distribution of the tick vector due to climate change, habitat disruption or bird 359 migration 127,128 . The pathogen has a wide host range and humans can become exposed through tick 360 bites, or by exposure to body fluids from viremic livestock or humans. Outbreaks in hospital settings have 361 also been reported 129 . The high mortality (4-40%), and a lack of licensed vaccine or treatment highlights 362 the urgency for vaccine development (TABLE. 1) . However, to date this has been hampered by limited 363 availability of immunocompetent models to fully evaluate vaccine efficacy, and a lack of information 364 regarding correlates of protection. Furthermore, differences in the ability of distinct vaccine platforms 365 delivering CCHFV antigens to confer protection have been reported 130-132 , suggesting that a specific 366 phenotype of immunity may be preferential (i.e., particular IgG subclass, or phenotype of antigen-specific 367 T-cell), or that an effective design approach should consider targeting multiple antigens simultaneously. during outbreaks of ANDV are of increasing concern 140 . The precise correlates of protection from infection 394

have not been conclusively identified. As for LASV and CCHFV, the surface glycoprotein precursor GPC, 395 which is co-translationally cleaved into the Gn and Gc envelope proteins, is considered to be an important 396 target for protective immunity. However, the multifunctional nucleoprotein (N) can also elicit cellular and 397 humoral immune responses and as such, may represent an additional antigen target. regimen, yet animals were completely protected from mortality. There was an association with increased 408 control of ANDV replication following challenge in hamsters when immunized with Ad5-Gn > Ad5-Gc. 409

When Ad5-Gn and Ad5-Gc were co-administered, ANDV RNA was undetectable in challenged animals. 410

be transmitted by multiple mosquito species. It has largely affected sub-Saharan Africa to date, but is 412 expanding geographically, with outbreaks spreading to the Arabian Peninsula and Madagascar. A 413 member of Phenuiviridae family, order Bunyavirales, its structure is similar to CCHFV: it possesses an 414 envelope and contains a tripartite, ambisense negative sense RNA viral genome (Fig. 3C) . RVFV 415 infection predominantly affects ruminants with high rates of mortality, and it is responsible for mass 416 spontaneous abortions and neonatal mortality, with substantial economic impact. The finding that RVFV 417 can infect placental tissue 142 has raised concerns that infection may also be associated with risk of 418 miscarriage in human pregnancy 143 . Infection of humans can be as a result of contact with infected 419 animals, or through mosquito bites during high density circulation in animals 144 . Clinical symptoms are 420 wide-ranging, but can be severe, resulting in hemorrhagic fever with mortality rates of up to 35% in 421 hospitalized patients 144 (TABLE. 1). It is important to note that this virus also has biosecurity implications 422 due to the fact that it can be lethal in aerosolized form, and thus it represents a threat for bioterrorism 144 . 423

There are no licensed vaccines for human use, and veterinary vaccines have been associated with some 424 safety issues (i.e., fetal malformations/stillbirths) and are deemed unsafe for use in humans 145 . As such, 425 a one-health approach for safe and effective vaccine development would be a worthy consideration. 426

NAbs are considered to be crucial for conferring sterilizing protection, and in particular NAbs directed Ab titers sustained out to week 26 post-immunization, and complete protection from challenge at week 436 27. In the context of prior immunity to Ad5, the authors demonstrated that pre-existing immunity had a 437 negative impact on Ab titers and survival when a low dose Ad5-GnGc was used (10 6 PFU), although this 438 could be largely overcome by increasing the dose of vaccine used to immunize (10 8 PFU). 439

Subsequent pre-clinical studies have evaluated ChAdOx1 as a vaccine against RVFV. A head-to-head 440 comparison of immunogenicity and efficacy was described for i.m immunization with 1 x 10 8 IU of 441 ChAdOx1 or Ad5 encoding Gn and Gc 148 . In addition, the effect of co-administration with commercial 442 adjuvants AddaVax TM and Matrix-M TM was evaluated. As previously observed, humoral immune 443 responses elicited by Ad5 were superior to ChAdOx1 112,149 , with higher NAb titers detected in Ad5-GnGc 444 immunized mice. However, adjuvants enhanced NAb responses elicited by ChAdOx1-GnGc, but not Ad5-445

GnGc. In contrast, AddaVax TM (but not Matrix-M TM ) enhanced CD8 + IFN-γ + and TNF responses in Ad5-446

GnGc immunized mice, but had no effect on the cytokine profile elicited by ChAdOx1-GnGc. These 447 differences highlight that distinct, underlying mechanisms likely contribute to the induction of humoral or 448 cellular immunity induced by these Ad platforms 9 . Despite differences, both platforms conferred 100% 449 protection from challenge with 1 x 10 3 PFU of RVFV strain 56/74 administered i.p. 450

Considering that a one-health approach is an appealing strategy for a vaccine against RVFV, studies 451 have shown that the ChAdOx1-GnGc vaccine can elicit protective immunity in sheep, goats and cattle 150 , 452 and importantly, in pregnant sheep and goats 145 . A single-shot i.m immunization with 1 x 10 9 IU elicited 453

NAb responses in all three species, and conferred 100% protection from challenge with no detectable 454 viremia. In pregnant ruminants immunized in the first trimester, the vaccine was shown to elicit robust 455

NAb titers, and provide protection against viremia and prevent fetal loss, although the latter was 456 incomplete in goats, with two out of 23 fetuses found to be autolyzed (1/5 and 1/3 in two does with multi-457 fetal pregnancies). Interestingly, NAb titers were higher in goats with fetal loss as compared with sheep 458 where no fetal loss was observed, suggesting that species-specific differences in mechanisms of in utero 459 infection or the phenotype of protective immunity may play a role in vaccine efficacy. 460

The TPP for vaccines against RVFV include three options: (i) a human vaccine for reactive, emergency 461 use to be deployed during outbreaks and in regions in close proximity to outbreaks which is safe for use 462 during pregnancy, (ii) a vaccine which could confer longer-term protection for individuals with high risk of 463 infection due to their occupation (i.e., slaughterhouse workers, veterinarians, farmers), and (iii) a vaccine 464 suitable for use in ruminants which could prevent transmission to between animals and to humans. The 465 latter TPP should be affordable, suitable for use in pregnant animals, independent of cold-chain storage 466 requirements and compatible with DIVA principles (differentiating infected from vaccinated animals). In 467 terms of a vaccine for humans, the optimal criteria include at least 90% efficacy in preventing disease, 468 rapid onset of immunity (2 weeks), the ability to confer protection against all RVFV lineages for at least 1 469

year following a single dose regimen, and suitability for co-administration with other relevant vaccines. in spread to over 70 countries and its declaration as a public health emergency of international concern 476 by the WHO. Transmitted by infected mosquitoes of the Aedes species, the majority of cases are 477 asymptomatic, but the virus can cause a spectrum of fetal and birth defects collectively known as 478 congenital Zika syndrome, and infection has been associated with Guillain-Barré syndrome (GBS). ZIKV 479 is an enveloped, positive sense RNA virus in the family Flaviviridae and order Amarillovirales (Fig. 3D) . 480

The family includes other viruses which can cause hemorrhagic fever or encephalitis, such as Dengue 481 virus (DENV), West Nile virus (WNV) or Japanese Encephalitis virus (JEV). In 2016, a dramatic increase 482 in cases of microcephaly and other congenital or neurological disorders was associated with infection 483 with ZIKV during pregnancy in Brazil. As the arthropod vector, Aedes mosquitoes, has a broad 484 geographic distribution, there is concern that ZIKV could spread to the Northern hemisphere (TABLE. 1) . 485

As such, the development of an effective vaccine which is safe for use in individuals of child-bearing age 486 or in pregnant people, is a public-health priority. 487

Antigens which have been evaluated as vaccine targets for ZIKA include the pre-membrane (prM) or 488 envelope (E) proteins which are exposed on the surface of the virion (Fig. 2D) . In late 2016, Abbink and 489 colleagues described the construction of a species G simian Ad vaccine platform, RhAd52 152 , encoding 490 ZIKV prM-Env 153 . A single-shot regimen was tested in rhesus monkeys following i.m immunization with 1 491

x 10 11 v.p. The Ad vaccine rapidly induced ZIKV Env-specific NAbs two weeks post-immunization with 492 broad epitope recognition, along with Env-specific T-cell responses. Importantly, 100% protection from 493 complete protection against subcutaneous (s.c) challenge with 10 3 PFU of ZIKV-BR was observed. 494

Subsequently, an Ad26-based vaccine, a species D Ad vector, encoding membrane (M) and Env was 495 evaluated in mice and NHP. In both species, Env binding and NAbs were detected, and a single-shot low This modified antigen was encoded within Ad5, and used to immunize mice s.c with 1 x 10 11 v.p, with a 507 homologous vector boost administered via i.n, or intradermal (i.d) route on D14 post-prime. As described 508

for other Ad platforms 104,112 , rapid induction of ZIKV-specific Abs was detected two weeks post-509 immunization, and NAbs were high one month following the boost immunization. Interestingly, this study 510 evaluated protection from disease in ZIKV challenged pups born to immunized mice. Complete survival 511 was observed in pups from immunized mice, versus 12.5% survival pups from PBS immunized mothers. 512

Furthermore, in the Ad-immunized groups pups displayed only mild to no symptoms of neurological 513 disease (i.e., hindlimb paralysis), whereas all pups of PBS immunized dams had neurological disease 514

Although prior studies with DNA-based vaccines identified the optimal prM-Env cassette for use in 516

RhAd52-prM-Env (which retains the TM domain of Env), a separate study determined that prM-EnvΔTM 517 was the optimal antigen configuration when used in ChAdOx1 154 . ChAdOx1-based vaccines, with various 518 iterations of the prM-Env cassette were tested i.m at a dose of 1 x 10 8 IU in mice. ChAdOx1-prM-EnvΔTM 519 elicited NAbs which were maintained for 16 weeks following a single-shot, and immunization conferred 520 100% protection from challenge. In a more recent study, the authors evaluated the same ChAdOx1 521 vaccine platform, encoding the envelope protein domain III (EDIII) as a sole antigen, on the basis that 522 this domain has previously been reported to be an effective immunogen for other flaviviruses 155 . However, 523 despite inducing anti-ENV Abs, NAbs were not elicited and the vaccine candidate failed to control viremia, 524 or completely protect against challenge in two mouse models 156 , suggesting that EDIII is not an optimal 525 vaccine target for protection against ZIKV. 526

The WHO TPP for a priority vaccine against ZIKV is one which could be used predominantly in an 527 outbreak response, with the main objective being the prevention of pre-natal ZIKV infection, and in 528 preventing of clinical illness, namely congenital malformations or complications in pregnancy. The ideal 529 vaccine would be expected to prevent virologically confirmed disease in >80% of the population, in a 530 single dose formulation using a non-replicating platform, and should be capable of neutralizing both the 531 Asian and African ZIKV lineages. Additional considerations include suitability for co-administration with 532 other appropriate licensed vaccines (i.e., the WHO EPI program), manufacturing processes in place for 533 rapid scale up, affordability and shelf-life stability, allowing cold-chain free distribution. Although NAbs 534 are considered to be an important correlate of protection, there is growing appreciation that CD8 + T-cells 535 might also contribute to protection 157,158 . Ad-based vaccines are known to elicit potent CD8 + 536 responses 9,159,160 , in addition to Ab, and as previously stated, can exhibit breadth of reactivity. 537

Furthermore, the platform fulfils requirements for co-administration with EPI vaccines 79 , and the capacity 538 for rapid scale up to meet demand during outbreak scenarios. 539

The urgent need for rapid-response vaccines to curtail the global spread of SARS-CoV-2, put 540 vaccines based on Ad5, Ad26 and ChAdOx1 were constructed, manufactured, and rapidly advanced to 546 safety and efficacy studies in early 2020. Several reviews describing the immunogenicity and efficacy of 547

Ad-based vaccines against SARS-CoV-2 have been published 22,86 , and will not be covered in detail in 548 this review. However, as global-scale evaluation of Ad vaccines has provided a wealth of information 549 regarding the clinical safety profile of distinct Ad-based vectors, we will summarize the latter findings, as 550 they will inform the design of next-generation Ad vaccine platforms for emerging infectious diseases. 551

The rationale for use of ChAdOx1 as a vaccine against SARS-CoV-2 was based on its low 552 seroprevalence in humans 167 , its prior evaluation in Phase I clinical trials as a vaccine for other viral 553 local adverse responses recorded during the first 7 days post-vaccination, the most common were mild 570 tenderness, which was reported by 83% of participants, and pain at the injection site (reported by 67% 571 of participants). Mild to moderate fatigue (70% of participants), headache (68%), malaise (61%), and 572 muscle ache (60%), followed by chills and feeling feverish, were among the most common systemic 573 adverse reactions reported within 7 days of ChAdOx1 vaccine administration 77 . In a two-dose regimen, 574

where prime vaccine administration was followed by a boost 28 days later, mild to moderate pain and 575 tenderness remained the most common local adverse reaction, while headache, feeling feverish, chills, 576 malaise, and muscle pain were reported as the most common systemic adverse reactions, similar to 577 participants who received only a single dose of the vaccine. In a two-dose cohort, it was noticed that the 578 reactogenicity profile (or the severity of adverse reactions) after administration of a booster dose of the 579 vaccine was less severe, as compared to the severity of adverse reactions after the prime dose 580

In a recent report of data collected from the ongoing pivotal double-blind, placebo-controlled Phase-III 582 study, the safety and efficacy of AZD1222 was evaluated in 21,587 participants who received AZD1222 583 in a prime-boost regimen, and in 10,792 participants who received placebo (NCT04516746) 171 . 584

Unsolicited adverse events (AEs) were recorded for a duration of 28 days after each dose of vaccine or 585 placebo, while solicited local and systemic AEs were monitored for 7 days post-administration of vaccine 586 or placebo. This study evaluated the safety and efficacy of a vaccine dose of 5 x 10 10 v.p following i.m 587 administration, with a 4-week interval between prime and boost immunizations. Participants were also 588 stratified by age into those who were 18-65 years old, and those who were over 65 years of age. The 589 majority of participants in this study had comorbidities that are known to increase COVID19 disease 590 severity, including a history of obesity, Type 1 and Type 2 diabetes, high blood pressure and history of 591 smoking, among others. Similar to findings from earlier trials, the majority of solicited local AEs were mild 592 to moderate in intensity, with tenderness (68.7%) and pain at the injection site (58.3%). Upon analysis of 593 systemic AEs, in addition to mild and moderate fatigue, muscle pain and headache observed in earlier 594 clinical trials with AZD1222, in this larger trial, severe fatigue, muscle pain, headache, and malaise were 595 observed in a subset of participants aged 18-65 years after the first vaccine dose 171 . However, the 596 majority of local and systemic AEs were self-limiting and resolved within 1 to 2 days after the onset. 597

The analysis of vaccine reactogenicity in this larger cohort of participants revealed a spectrum of rare 598 unsolicited AEs, which were observed within 28 days after vaccine administration. Out of 21,587 599 participants who received at least one dose of the vaccine, 225 participants reported AEs of Grade 3 or 600 higher, 1288 participants (6%) experienced medically-attended AEs, and AEs of special interest observed 601 in 58 participants were judged to be related to trial intervention. However, it is important to note that 602

Grade 3 AEs, medically-attended and AEs of special interest, were also observed in participants receiving 603 the placebo at similar frequencies. Furthermore, the absolute majority of various types of medically-604 attended AEs were experienced only by a single patient and were observed in both the vaccine and 605 placebo arms, making formal association of each particular type of AE with vaccine reactogenicity 606 impossible. Vaccine reactogenicity was stronger after the first administration, compared to a subsequent 607 boost dose and was less severe in participants over 65 years of age, compared to vaccines from 18-65 608 years old group. Overall, this and other clinical trials that analyzed the safety and efficacy of AZD1222 609 vaccine concluded that the vaccine was safe and effective at preventing symptomatic and severe 610 groups. In this study, participants of 18-55 years of age reported fever as a frequent solicited AE. In this 627 age group, 15% of participants in the low vaccine dose group and 39% of participants in the high dose 628 group reported grade 1 and 2 fevers. Grade 3 fever was reported by 5% and 9% of participants after 629 receiving low and high vaccine doses, respectively. In a group of 65 years and older, grade 3 fever was 630 not observed in participants who received low dose of the vaccine, and was observed in 1% of 631 participants who received high vaccine dose. After the second dose of the vaccine, no grade 3 fever was 632 observed in any of the groups and there was no participant discontinuation due to an AE 175 . 633

In a subsequent randomized, double-blind, placebo-controlled Phase III clinical trial of the Ad26.COV2.S 634 COVID-19 vaccine administered at a single dose of 5 x 10 10 v.p, the safety and efficacy was evaluated 635 in 19,630 participants who received the vaccine, and in 19,691 participants who received placebo 636 (NCT04505722) 56 . In this study, participants were also stratified by age into two groups: 18-59 years old, reported unsolicited AEs of grade 3 or higher, which were considered to be related to the intervention 56 . 647

Although an imbalance in the number of unsolicited AEs between vaccine and placebo groups were 648 noted, the majority of these events were only observed in a single patient, making definitive conclusion 649 regarding association of the event with vaccine administration impossible. Similar to findings for the 650 AZD1222 vaccine, the reactogenicity of a single-dose of the Ad26.COV2.S vaccine was less pronounced 651 in participants aged 60 years and older, as compared with a cohort of participants 18-59 years old. In 652 summary, a single-dose of the Ad26.COV2.S vaccine was found to be well-tolerated and safe in humans. 653

Vaccines to combat COVID-19 based on the common human adenovirus serotype, Ad5, were developed 654 (CanSino Biologics), and evaluated for safety and efficacy in China (NCT04313127) 176 . In a Phase I dose-655 escalation, open-label, non-randomized clinical trial, reactogenicity was evaluated in three cohorts of 656 participants who received 5 x 10 10 v.p (low-dose cohort, 36 participants), 1 x 10 11 v.p (middle-dose cohort, 657 36 participants), and 1.5 x 10 11 v.p (high-dose cohort, 36 participants) 176 . Although the frequency of all 658

reported AEs was similar in all cohorts, Grade 3 AEs were more common in participants who received 659 the highest vaccine dose. While pain at the injection site was the most frequent local AE, observed in 660 47% of participants in the low-dose, 56% of participants in the middle-dose, and in 58% of participants in 661 the high-dose cohorts, fever, followed by headache, fatigue, and muscle pain were the most frequently 662 recorded systemic AEs. Specifically, fever was observed in 42% of participants who received the low 663 dose, 42% who received the middle dose, and in 56% of participants, who received the high vaccine 664 dose. In this trial, Grade 3 fever was observed in 14% of participants who received the high dose of the 665 vaccine, while 6% of participants who received low and middle vaccine doses reported Grade 3 fever. 666

Overall, the reactogenicity of the Ad5-based vaccine was judged to be dose-dependent, and subsequent 667

Phase II and III clinical trials were initiated with only low and middle doses of the vaccine. 668

In the subsequent randomized, double-blind, placebo-controlled Phase II clinical trial, the Ad5-based 669 COVID-19 vaccine was administered at a dose of 5 x 10 10 v.p (129 participants) or 1 x 10 11 v.p (253 670 participants), and vaccine reactogenicity was compared to placebo (126 participants). In this larger trial, 671 the dose-dependent increase in the severity of AEs was documented and was determined to be highly 672 statistically significant (NCT04341389) 176 . Specifically, while the majority of reported adverse reactions 673 were mild to moderate in severity, grade 3 adverse reactions were noted in 9% of participants who 674 received vaccine dose of 1 x 10 11 v.p, which was significantly higher than in participants who received 5 675

x 10 10 v.p of the vaccine (1% of participants, p=0.0011), or placebo (0% participants, p=0.0004). Similar 676 to findings in the Phase I trial described above (NCT04313127) 177 , fever was the most frequently reported 677 grade 3 adverse reaction, while fatigue was reported as the most frequent systemic adverse reaction: 678 observed in 42% of participants who received 1 x 10 11 v.p vaccine dose, and in 34% of participants who 679

received 5 x 10 10 v.p dose of the vaccine. In this study, it was noted that high levels of pre-existing anti-680

Ad5 immunity, older age, and male sex, were associated with a significantly lower frequency of fever after Ad5-based COVID-19 vaccine in 20,000 participants who will receive a single dose of vaccine or placebo, 686 is due for reporting in early 2022 (NCT04526990). 687 reported headache, and 20% reported muscle pain, all of which were mild in severity. However, in this 721 group of vaccinees, muscle pain was reported by 27% of responders as moderate, 10% as severe, and 722 1% as grade 4. However, because this observational study was small and did not include a placebo 723 group, a definitive conclusion on the association of these severe AEs with vaccine administration could 724 not be drawn. 725

Although Ad-based vaccines displayed good tolerability and safety in clinical trials that included tens of 726 thousands of participants, administering Ad26.COV2.S and ChAdOx1 (but not Ad5) vaccines to millions 727 of people revealed some extremely rare serious AEs that were suspected to be causally-associated with with uncircumcised men with pre-existing Ad5-specific immunity found to be at highest risk [198] [199] [200] . 796 

A hierarchy in immunogenicity has been observed when comparing two-dose mRNA vaccines (mRNA-812 1273, BNT162b2) versus single-dose Ad26.COV2.S, with mRNA-1273 > BNT162b2 > Ad26.COV2.S 207 . 813

In agreement with this, Ad-based vaccination regimens have been shown to elicit lower NAb titers (when 814 measured 4 weeks after full vaccination) than mRNA-based vaccines, with reduced NAb titers against 815 variants of concern (VOCs) also observed for Ad platforms versus mRNA 208 . Overall efficacy in preventing 816 symptomatic infection for Ad-based vaccines has also been reported to be lower than for mRNA vaccines 817 (60-70% versus >90%) 171,208-211 . However, importantly, protection from severe-critical disease, 818 hospitalization or death is high for all vaccine platforms. In a Phase III efficacy study with a single-dose 819 of Ad26.COV2.S, protection against severe-critical COVID-19 disease >28 days post-immunization was 820 85.4% 56 , and efficacy against severe disease (i.e., emergency department visits) was reported to be 821 ~94% for ChAdOx1 AZD1222 171 , and 91.6% for Sputnik V 178 . Furthermore, real world protection data are 822 now emerging. A non-randomized study of U.S insurance claim data reported vaccine effectiveness (VE) 823 of 81% against COVID-19 hospitalization following a single-shot of Ad26. More recently, the Janssen Ad26.COV2.S vaccine has been tested in a homologous boost regimen. 830

Press releases for the ENSEMBLE 2 study, in which a boost of Ad26.COV2.S was administered at a two 831 month interval, have suggested VE of 100% against COVID-19 hospitalization. Very recently, results from 832 the Sisonke 2 Phase 3b study were reported, indicating that a booster shot of Ad26.COV2.S administered 833 6-9 months following initial immunization of South African healthcare workers, has a VE >84% against 834 hospital admission when the Omicron variant was dominant 214 . Although overall, the VE of Ad26.CoV2.S 835 has been reported to be lower than mRNA vaccines 207 , there is evidence of waning protection from 836 infection or hospitalization for mRNA vaccines, whereas VE for Ad26.COV2.S appears to be durable 215 . 837

Data are still emerging regarding efficacy/VE against new VOC. Nonetheless, the robust protection from 838 severe disease for each vaccine, despite differences in immunological potency, suggests a need to better 839 understand the qualitative differences between the immune response elicited by Ad/mRNA platforms in 840 the future, and how those parameters translate into correlates of protection. 841

Through the course of the pandemic, several priority areas for pandemic preparedness have become 842 apparent. First, it is clear that we need to (i) optimize and develop vaccines capable of conferring broad, 843 protective immunity which could address the emergence of variants. In the context of Ad-based vaccines, 844 this could be achieved by applying strategies used in "universal" vaccine development, such as focusing 845 on highly conserved viral antigens or epitopes/domains, incorporating molecular or genetic adjuvants, or 846 engineering multi-valent vectors which encode more than one vaccine antigen, to increase breadth of 847 protection. Related to this is (ii) the crucial importance of antigen selection, and the potential for use of 848 stabilized immunogens -optimized through structure-guided approachesto elicit humoral immune 849 responses against antigenically authentic viral proteins. This was highlighted by reports of a -2P 850 stabilization modification in the spike (S) of SARS-CoV-2, which locked it into a pre-fusion structure and 851 enhanced expression 216,217 . This approach was used by both mRNA platforms, in addition to J&J's 852

Ad26.COV2.S vaccine 217 , but was not used in the ChAdOx1 AZD1222 platform. Although it is difficult to 853 evaluate how differences in antigen design could contribute to differences in efficacy when comparing 854 between two distinct Ad platforms, these questions can be considered for the design of next-generation 855 vaccines against viruses which represent a future emerging pandemic threat. 856

In addition to these points, questions also arose which were related to (iii) increasing our understanding 857 of the precise, step-by-step mechanism of action of vaccines i.e., can we design optimized vaccines 858 which maximize prevention of infection, as well as vaccines which prevent disease? Further to this is the 859 need to better understand how homologous or heterologous Ad prime:boost regimens work (and indeed 860 heterologous Ad+mRNA, or +protein) 218-222 in terms of the phenotype of immune response they elicit, how 861 varying intervals between prime:boost affects the downstream immunogenicity or durability of immunity, 862 and how pre-existing immunity (i.e., to Ad vectors) affects subsequent homologous boosting. In addition, independent of specialized cold-chain, Ad-based vaccines represent an ideal platform for equitable 868 vaccine distribution. Efforts to build capacity in local vaccine manufacturing within LMICs will undoubtedly 869 help to overcome supply issues, and will be vital for future pandemic preparedness. 870

A broad range of approaches can be taken to enhance the safety, immunogenicity and ultimately the 871 Coronaviruses, including SARS-CoV-1, SARS-CoV-2 and MERS-CoV have been omitted from this table due to the large amount of published data on these viruses. Emerging viruses from the Paramyxoviridae (i.e., Nipah Virus) have also been omitted due to space constraints. In this special issue on emerging infectious diseases, Coughlan, Kremer and Shayakhmetov review the history, safety, and real-world efficacy of adenovirus (Ad)-based vaccines. They also address how the development of Ad-based vaccines against other emerging viruses underpinned their use in response to the SARS-CoV-2 pandemic.

Measles 50 Years After Use of Measles Vaccine

Worldwide 906 trend in measles incidence from 1980 to 2016: A pooled analysis of evidence from 194 WHO 907 Member States

Broadly neutralizing hemagglutinin stalk-909 specific antibodies require FcgammaR interactions for protection against influenza virus in vivo

Broadly neutralizing anti-influenza 912 antibodies require Fc receptor engagement for in vivo protection

Safety, efficacy, and immunogenicity of VGX-3100, a 1053 therapeutic synthetic DNA vaccine targeting human papillomavirus 16 and 18 E6 and E7 proteins 1054 for cervical intraepithelial neoplasia 2/3: a randomised, double-blind, placebo-controlled phase 2b 1055 trial

Safety and Immunogenicity of an Anti-Zika 1058

Adenovirus-Extracellular Protein Interactions and Their Impact on 1060 Innate Immune Responses by Human Mononuclear Phagocytes

Lactoferrin Retargets Human Adenoviruses to TLR4 to Induce 1064 an Abortive NLRP3-Associated Pyroptotic Response in Human Phagocytes

Coagulation factor X activates innate 1068 immunity to human species C adenovirus

mRNA vaccines for infectious diseases: 1071 principles, delivery and clinical translation

Modified mRNA Influenza Virus Vaccine Provides Broad Protection in Mice

Construction of a defective 1080 adenovirus vector expressing the pseudorabies virus glycoprotein gp50 and its use as a live 1081 vaccine

Clinical assessment of a novel recombinant simian adenovirus ChAdOx1 as a vectored 1084 vaccine expressing conserved Influenza A antigens

A Monovalent Chimpanzee Adenovirus Ebola 1088 Vaccine Boosted with MVA

Safety and Efficacy of Single-Dose 1092

Vaccine against Covid-19

Phase 1 Study of Ad26.ZIKV.001, an Ad26-Vectored Anti-Zika Virus Vaccine

Heterologous Two-Dose Vaccination with Simian 1100

Adenovirus and Poxvirus Vectors Elicits Long-Lasting Cellular Immunity to Influenza Virus A in 1101 Healthy Adults

An AAV-based, room-temperature-stable, 1104 single-dose COVID-19 vaccine provides durable immunogenicity and protection in non-human 1105 primates

Self-Replicating RNA Viruses for Vaccine Development against Infectious 1107 Diseases and Cancer. Vaccines (Basel) (2021)

A Recombinant Vesicular Stomatitis Virus Ebola 1110 Vaccine

The effect of dose on the safety and 1113 immunogenicity of the VSV Ebola candidate vaccine: a randomised double-blind, placebo-1114 controlled phase 1/2 trial

A Newcastle disease virus expressing 1118 a stabilized spike protein of SARS-CoV-2 induces protective immune responses

Safety and Immunogenicity Analysis of a 1122

Newcastle Disease Virus (NDV-HXP-S) Expressing the Spike Protein of SARS-CoV-2 in Sprague 1123

Non-propagative human parainfluenza virus type 2 nasal 1126 vaccine robustly protects the upper and lower airways against SARS-CoV-2. iScience (2021)

First-in-Human Evaluation of the Safety 1130 and Immunogenicity of an Intranasally Administered Replication-Competent Sendai Virus-1131

Vectored HIV Type 1 Gag Vaccine: Induction of Potent T-Cell or Antibody Responses in Prime-1132 Boost Regimens

Single-cycle adenovirus vectors in the current vaccine landscape

Retargeting 1136 adenovirus serotype 48 fiber knob domain by peptide incorporation

Progress in Adenoviral Capsid-Display Vaccines

Chimpanzee 1141 adenoviral vectors as vaccines for outbreak pathogens

Vaccination with viral vectors expressing NP, M1 and chimeric 1145 hemagglutinin induces broad protection against influenza virus challenge in mice

First-in-Human Randomized Study to Assess the 1149 Safety and Immunogenicity of an Investigational Respiratory Syncytial Virus (RSV) Vaccine 1150 Based on Chimpanzee-Adenovirus-155 Viral Vector-Expressing RSV Fusion, Nucleocapsid, and 1151 Antitermination Viral Proteins in Healthy Adults

Vaccination With Viral Vectors 1155

Expressing Chimeric Hemagglutinin, NP and M1 Antigens Protects Ferrets Against Influenza 1156 Virus Challenge

Chimpanzee adenovirus-and MVA-1159 vectored respiratory syncytial virus vaccine is safe and immunogenic in adults

Safety and immunogenicity of an oral, 1163 replicating adenovirus serotype 4 vector vaccine for H5N1 influenza: a randomised, double-blind, 1164 placebo-controlled, phase 1 study

Evaluation of a mosaic HIV-1 vaccine in a 1168 multicentre, randomised, double-blind, placebo-controlled, phase 1/2a clinical trial (APPROACH) 1169 and in rhesus monkeys (NHP 13-19)

Safety and immunogenicity of the 1173 ChAdOx1 nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase 1/2, single-1174 blind, randomised controlled trial

Safety and Immunogenicity of ChAd63 1178 and MVA ME-TRAP in West African Children and Infants

Safety and Immunogenicity of Malaria Vectored 1182 Vaccines Given with Routine Expanded Program on Immunization Vaccines in Gambian Infants 1183 and Neonates: A Randomized Controlled Trial

Safety and immunogenicity of the ChAdOx1 nCoV-19 (AZD1222) 1187 vaccine against SARS-CoV-2 in HIV infection: a single

The safety and immunogenicity of an 1191 adenovirus type 35-vectored TB vaccine in HIV-infected, BCG-vaccinated adults with CD4(+) T 1192 cell counts >350 cells/mm(3)

Ebola vaccination in healthy and HIV-infected adults: A randomised, 1196 placebo-controlled Phase II clinical trial in Africa

Spray dried human and chimpanzee adenoviral-vectored vaccines 1200 are thermally stable and immunogenic in vivo

Long-term thermostabilization of live 1204 poxviral and adenoviral vaccine vectors at supraphysiological temperatures in carbohydrate 1205 glass

Stability of Chimpanzee Adenovirus Vectored Vaccines 1208 (ChAdOx1 and ChAdOx2) in Liquid and Lyophilised Formulations

Adenoviral vector vaccine platforms 1210 in the SARS-CoV-2 pandemic

Safety and immunogenicity of the two-dose 1213 heterologous Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen in children in Sierra Leone: 1214 a randomised, double-blind, controlled trial

Safety, reactogenicity, and immunogenicity of a 1218 chimpanzee adenovirus vectored Ebola vaccine in children in Africa: a randomised, observer-1219 blind, placebo-controlled, phase 2 trial

Safety, reactogenicity, and immunogenicity 1223 of a chimpanzee adenovirus vectored Ebola vaccine in adults in Africa: a randomised, observer-1224 blind, placebo-controlled, phase 2 trial

Adenovirus Type 26-and Modified Vaccinia Ankara-Vectored Ebola Vaccines: A Randomized 1229 Clinical Trial

Safety and long-term immunogenicity of the two-1232 dose heterologous Ad26.ZEBOV and MVA-BN-Filo Ebola vaccine regimen in adults in Sierra 1233 Leone: a combined open-label, non-randomised stage 1, and a randomised, double-blind, 1234 controlled stage 2 trial

Chimpanzee Adenovirus Vector Ebola 1237 Vaccine

A single dose of ChAdOx1 Chik 1240 vaccine induces neutralizing antibodies against four chikungunya virus lineages in a phase 1 1241 clinical trial

A replication-competent 1244 adenovirus-vectored influenza vaccine induces durable systemic and mucosal immunity

1247 Immunobiology of Ebola and Lassa virus infections

Ebola virus 1250 vaccine: benefit and risks of adenovirus-based vectors

Ebola Virus Disease Complications as Experienced by 1254 Survivors in Sierra Leone

Early clinical sequelae of Ebola virus disease in Sierra 1257 Leone: a cross-sectional study

Fruit bats as reservoirs of Ebola virus

Serostatus cutoff levels and fold increase to define seroresponse to recombinant vesicular 1264 stomatitis virus -Zaire Ebola virus envelope glycoprotein vaccine: An evidence-based analysis

Development of a 1267 preventive vaccine for Ebola virus infection in primates

Chimpanzee adenovirus vaccine 1271 generates acute and durable protective immunity against ebolavirus challenge

CD8+ cellular immunity mediates rAd5 vaccine 1275 protection against Ebola virus infection of nonhuman primates

Accelerated vaccination for Ebola virus haemorrhagic fever in 1279 non-human primates

Preventative 1281 Vaccines for Zika Virus Outbreak: Preliminary Evaluation

Enhanced protection against Ebola virus mediated by an improved adenovirus-1285 based vaccine

Immune protection of nonhuman 1288 primates against Ebola virus with single low-dose adenovirus vectors encoding modified GPs

Airway delivery of an adenovirus-1291 based Ebola virus vaccine bypasses existing immunity to homologous adenovirus in nonhuman 1292 primates

Mucosal delivery of adenovirus-based vaccine protects against Ebola virus 1295 infection in mice

A single sublingual dose of an adenovirus-based vaccine protects against lethal Ebola 1298 challenge in mice and guinea pigs

Intranasal immunization with 1300 an adenovirus vaccine protects guinea pigs from Ebola virus transmission by infected animals

EVs Improves the In Vivo Immunogenicity of Human and Non-human Adenoviral Vaccines in 1305

Chimpanzee adenoviral vector prime-boost regimen elicits potent immune responses against 1308 Ebola virus in mice and rhesus macaques

Ad35 and ad26 vaccine vectors induce potent 1312 and cross-reactive antibody and T-cell responses to multiple filovirus species

A Multi-Filovirus Vaccine Candidate: Co-1316 Expression of Ebola, Sudan, and Marburg Antigens in a Single Vector

Complete protection of the BALB/c and C57BL/6J mice against 1320

Ebola and Marburg virus lethal challenges by pan-filovirus T-cell epigraph vaccine

A prospective study of 1323 maternal and fetal outcome in acute Lassa fever infection during pregnancy

Early and strong immune responses are associated with control of 1327 viral replication and recovery in lassa virus-infected cynomolgus monkeys

Adenoviral vector-based vaccine is fully 1331 protective against lethal Lassa fever challenge in Hartley guinea pigs

ChAdOx1-1335 vectored Lassa fever vaccine elicits a robust cellular and humoral immune response and protects 1336 guinea pigs against lethal Lassa virus challenge

A single-shot adenoviral vaccine 1340 provides hemagglutinin stalk-mediated protection against heterosubtypic influenza challenge in 1341 mice

Prolonged evolution of the memory B cell response 1344 induced by a replicating adenovirus-influenza H5 vaccine

Vaccine vectors derived from a large collection of simian 1348 adenoviruses induce potent cellular immunity across multiple species

Differential Kinetics of Immune Responses 1352 Elicited by Covid-19 Vaccines

Novel adenovirus-based vaccines induce broad and sustained 1356 T cell responses to HCV in man

Vaccine platforms for the prevention of Lassa fever

Nucleocapsid protein-1361 based vaccine provides protection in mice against lethal Crimean-Congo hemorrhagic fever virus 1362 challenge

Development of vaccines against Crimean-Congo 1364 haemorrhagic fever virus

hemorrhagic fever: history, epidemiology, pathogenesis, clinical syndrome and 1367 genetic diversity

Immunization with DNA Plasmids 1370 Coding for Crimean-Congo Hemorrhagic Fever Virus Capsid and Envelope Proteins and/or Virus-1371

Like Particles Induces Protection and Survival in Challenged Mice

Crimean-Congo Hemorrhagic Fever Virus Subunit Vaccines Induce High 1375 Levels of Neutralizing Antibodies But No Protection in STAT1 Knockout Mice. Vector Borne 1376 Zoonotic Dis

Congo hemorrhagic fever (CCHF) 1379 viral vaccine expressing nucleoprotein is immunogenic but fails to confer protection against lethal 1380 disease

The complete genome analysis of Crimean-Congo hemorrhagic 1383 fever virus isolated in Turkey

A lethal disease model for 1386 hantavirus pulmonary syndrome

Structural basis of synergistic 1389 neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies

Protective neutralizing 1393 antibodies from human survivors of Crimean-Congo hemorrhagic fever

Hemorrhagic Fever Virus GP38

Adenovirus vectors expressing hantavirus proteins protect hamsters against 1400 lethal challenge with andes virus

Induction of Hantaan virus-specific immune responses in C57BL/6 mice by 1403 immunization with a modified recombinant adenovirus containing the chimeric gene, GcS0.7. Int 1404

Person-to-person transmission of Andes virus

Recombinant adenovirus vector 1409 vaccine induces stronger cytotoxic T-cell responses than recombinant vaccinia virus vector, 1410 plasmid DNA, or a combination of these

Rift Valley fever virus induces fetal demise in Sprague-Dawley rats 1414 through direct placental infection

Rift Valley Fever: a Threat to Pregnant Women Hiding in Plain 1416 Sight?

A complex adenovirus-vectored vaccine against 1419

Rift Valley fever virus protects mice against lethal infection in the presence of preexisting vector 1420 immunity

ChAdOx1 RVF vaccine against Rift Valley fever in pregnant sheep and goats

Current Status of Rift 1430 Valley Fever Vaccine Development. Vaccines (Basel

Immunogenicity and 1433 efficacy of a chimpanzee adenovirus-vectored Rift Valley fever vaccine in mice

Differential immunogenicity between HAdV-5 and chimpanzee adenovirus vector ChAdOx1 1437 is independent of fiber and penton RGD loop sequences in mice

Chimpanzee Adenovirus Vaccine Provides 1441

Zika Virus Infection -After the Pandemic

Construction and evaluation of 1447 novel rhesus monkey adenovirus vaccine vectors

Protective efficacy of multiple vaccine 1451 platforms against Zika virus challenge in rhesus monkeys

Rational Zika vaccine 1455 design via the modulation of antigen membrane anchors in chimpanzee adenoviral vectors

Identification of neutralizing epitopes within structural domain III 1458 of the West Nile virus envelope protein

Immunogenicity and 1462 Efficacy of Zika Virus Envelope Domain III in DNA, Protein, and ChAdOx1 Adenoviral

Vaccines (Basel) (2020)

Adenoviral vector type 26 encoding Zika virus 1466 (ZIKV) M-Env antigen induces humoral and cellular immune responses and protects mice and 1467 nonhuman primates against ZIKV challenge

Mapping and Role of the CD8(+) T Cell Response During Primary 1471 Zika Virus Infection in Mice

Adenoviral vectors persist in vivo 1475 and maintain activated CD8+ T cells: implications for their use as vaccines

Comparative analysis of the magnitude, quality, 1479 phenotype, and protective capacity of simian immunodeficiency virus gag-specific CD8+ T cells 1480 following human-, simian-, and chimpanzee-derived recombinant adenoviral vector immunization

First-in-human evaluation of the safety and 1484 immunogenicity of a recombinant adenovirus serotype 26 HIV-1 Env vaccine (IPCAVD 001)

Immunity duration of a recombinant adenovirus type-5 vector-based Ebola vaccine 1488 and a homologous prime-boost immunisation in healthy adults in China: final report of a 1489 randomised, double-blind, placebo-controlled, phase 1 trial

Safety and immunogenicity of a novel recombinant adenovirus type-5 vector-1493 based Ebola vaccine in healthy adults in China: preliminary report of a randomised, double-blind, 1494 placebo-controlled, phase 1 trial

Prevention of Respiratory Syncytial Virus 1498 Infection in Healthy Adults by a Single Immunization of Ad26.RSV.preF in a Human Challenge 1499 Study

Immunogenicity Study of a Respiratory Syncytial Virus Vaccine With an Adenovirus 26 Vector 1503

Encoding Prefusion F (Ad26.RSV.preF) in Adults Aged >/=60 Years

Safety and immunogenicity of a candidate Middle 1507 East respiratory syndrome coronavirus viral-vectored vaccine: a dose-escalation, open-label, 1508 non-randomised, uncontrolled, phase 1 trial

A novel chimpanzee adenovirus vector with low human seroprevalence: 1512 improved systems for vector derivation and comparative immunogenicity

ChAdOx1 and MVA based vaccine 1516 candidates against MERS-CoV elicit neutralising antibodies and cellular immune responses in 1517 mice

Protective efficacy of a novel simian 1520 adenovirus vaccine against lethal MERS-CoV challenge in a transgenic human DPP4 mouse 1521 model

Humoral Immunogenicity and Efficacy of 1524 a Single Dose of ChAdOx1 MERS Vaccine Candidate in Dromedary Camels

Phase 3 Safety and Efficacy of AZD1222 (ChAdOx1 1528 nCoV-19) Covid-19 Vaccine

Safety and 1531 Reactogenicity of the ChAdOx1 (AZD1222) COVID-19 Vaccine in Saudi Arabia

Safety and efficacy of the ChAdOx1 nCoV-1535 19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled 1536 trials in Brazil, South Africa, and the UK

A review of 65 years of 1540 human adenovirus seroprevalence

Interim Results of a Phase 1-2a Trial of 1544

Covid-19 Vaccine

Immunogenicity and safety of a recombinant adenovirus type-5-1548 vectored COVID-19 vaccine in healthy adults aged 18 years or older: a randomised, double-blind, 1549 placebo-controlled, phase 2 trial

Safety, tolerability, and immunogenicity of a recombinant adenovirus 1553 type-5 vectored COVID-19 vaccine: a dose-escalation, open-label, non-randomised, first-in-1554 human trial

Safety and efficacy of an rAd26 and rAd5 vector-based heterologous prime-boost COVID-19 1558 vaccine: an interim analysis of a randomised controlled phase 3 trial in Russia

Side effects and 1562 Immunogenicity following administration of the Sputnik V COVID-19 vaccine in health care 1563 workers in Iran

Active monitoring of early safety 1566 of Sputnik V vaccine in

Thrombosis and 1569 Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination

Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination

Fatal systemic inflammatory response syndrome in a ornithine transcarbamylase 1576 deficient patient following adenoviral gene transfer

A Phase 1 Trial of Oncolytic Adenovirus 1580 ICOVIR-5 Administered Intravenously to Cutaneous and Uveal Melanoma Patients

Mechanisms of Immunothrombosis in Vaccine-1583

Induced Thrombotic Thrombocytopenia (VITT) Compared to Natural SARS-CoV-2 Infection

Clinical Features of Vaccine-Induced Immune Thrombocytopenia and 1587 Thrombosis

Arterial events, venous thromboembolism, 1590 thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca ChAdOx1-S in 1591 Denmark and Norway: population based cohort study

US Case Reports of Cerebral Venous Sinus Thrombosis 1595

With Thrombocytopenia After Ad26.COV2.S Vaccination

Cerebral venous 1600 thrombosis and portal vein thrombosis: A retrospective cohort study of 537

Cerebral Vein Thrombosis With Vaccine-Induced Immune 1604 Thrombotic Thrombocytopenia

Cerebral venous thrombosis after vaccination 1608 against COVID-19 in the UK: a multicentre cohort study

Guillain-Barre syndrome

Syndrome Associated with COVID-19 Vaccination

Use of adenovirus type-5 1616 vectored vaccines: a cautionary tale

Efficacy assessment of a cell-mediated immunity 1620 HIV-1 vaccine (the Step Study): a double-blind, randomised, placebo-controlled, test-of-concept 1621 trial

Safety and efficacy of the HVTN 503/Phambili 1624 study of a clade-B-based HIV-1 vaccine in South Africa: a double-blind, randomised, placebo-1625 controlled test-of-concept phase 2b study

Recombinant adenovirus type 5 HIV gag/pol/nef 1629 vaccine in South Africa: unblinded, long-term follow-up of the phase 2b HVTN 503/Phambili study

Extended follow-up confirms early vaccine-enhanced 1633 risk of HIV acquisition and demonstrates waning effect over time among participants in a 1634 randomized trial of recombinant adenovirus HIV vaccine (Step Study)

Effect of rAd5-Vector HIV-1 Preventive Vaccines on HIV-1 1638 Acquisition: A Participant-Level Meta-Analysis of Randomized Trials

Continued Follow-Up of Phambili Phase 2b Randomized 1642 HIV-1 Vaccine Trial Participants Supports Increased HIV-1 Acquisition among Vaccinated Men

Adenovirus vector vaccination induces 1646 expansion of memory CD4 T cells with a mucosal homing phenotype that are readily susceptible 1647 to HIV-1

Activation of a dendritic cell-T cell axis by Ad5 immune 1649 complexes creates an improved environment for replication of HIV in T cells

Adenovirus-specific immunity after immunization 1653 with an Ad5 HIV-1 vaccine candidate in humans

Preexisting 1656 adenovirus seropositivity is not associated with increased HIV-1 acquisition in three HIV-1 vaccine 1657 efficacy trials

Serological immunity to 1660 adenovirus serotype 5 is not associated with risk of HIV infection: a case-control study

Comparative 1664 immunogenicity and effectiveness of mRNA-1273, BNT162b2 and Ad26.COV2.S COVID-19 1665 vaccines

Four SARS-CoV-2 vaccines 1668 induce quantitatively different antibody responses against SARS-CoV-2 variants

Safety and Efficacy of the BNT162b2 mRNA 1672

Covid-19 Vaccine

Efficacy and Safety of the mRNA-1273 SARS-CoV-2

Effectiveness of Covid-19 Vaccines against the 1678 B.1.617.2 (Delta) Variant

Effectiveness of the Single-Dose Ad26.COV2.S 1682 COVID Vaccine. medRxiv (2021)

Johnson & Johnson) Vaccines in Preventing COVID-19 Hospitalizations 1687

Among Adults Without Immunocompromising Conditions -United States

Vaccine effectiveness against hospital admission in South 1691 African health care workers who received a homologous booster of Ad26

Preliminary Results of the Sisonke 2 Study. medRxiv (2021)

Durability of Protection against COVID-19 Breakthrough 1696 Infections and Severe Disease by Vaccines in the United States. medRxiv (2022)

Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation

Ad26 vector-based 1703 COVID-19 vaccine encoding a prefusion-stabilized SARS-CoV-2 Spike immunogen induces 1704 potent humoral and cellular immune responses

Immunogenicity, safety, and 1708 reactogenicity of heterologous COVID-19 primary vaccination incorporating mRNA, viral-vector, 1709 and protein-adjuvant vaccines in the UK (Com-COV2): a single-blind, randomised, phase 2, non-1710 inferiority trial

Safety and immunogenicity of 1713 heterologous versus homologous prime-boost schedules with an adenoviral vectored and mRNA 1714 COVID-19 vaccine (Com-COV): a single-blind, randomised, non-inferiority trial

Immunogenicity and reactogenicity of heterologous 1721 ChAdOx1 nCoV-19/mRNA vaccination

Differential immunogenicity of homologous versus 1725 heterologous boost in Ad26.COV2.S vaccine recipients. medRxiv (2021)

A recombinant bovine adenoviral 1729 mucosal vaccine expressing mycobacterial antigen-85B generates robust protection against 1730 tuberculosis in mice

An intranasal vaccine durably protects against SARS-1733

CoV-2 variants in mice

Safety and immunogenicity of adenovirus-vectored nasal and epicutaneous 1736 influenza vaccines in humans

Safety and immunogenicity of novel respiratory 1740 syncytial virus (RSV) vaccines based on the RSV viral proteins F, N and M2-1 encoded by simian 1741 adenovirus (PanAd3-RSV) and MVA (MVA-RSV); protocol for an open-label, dose-escalation, 1742 single-centre, phase 1 clinical trial in healthy adults

Novel genetically-modified chimpanzee 1746 adenovirus and MVA-vectored respiratory syncytial virus vaccine safely boosts humoral and 1747 cellular immunity in healthy older adults

Novel Intranasal Influenza Vaccine (NasoVAX): A Phase 2 Randomized, Controlled Trial. 1752 Vaccines (Basel) (2021)

After the pandemic: perspectives on the future 1755 trajectory of COVID-19

ChAdOx1 interacts with CAR and PF4 with implications 1758 for thrombosis with thrombocytopenia syndrome

Biodistribution and retargeting of 1762 FX-binding ablated adenovirus serotype 5 vectors

Pros and Cons of Adenovirus-Based SARS-CoV-2 Vaccines

Operation Warp Speed: 1767 implications for global vaccine security

Reserving coronavirus disease 2019 vaccines for global access: cross 1770 sectional analysis

Reactogenicity and 1773 immunogenicity after a late second dose or a third dose of ChAdOx1 nCoV-19 in the UK: a 1774 substudy of two randomised controlled trials (COV001 and COV002)