key: cord-1025502-9nyfz7s2
authors: Müller, L.; Andree, M.; Moskorz, W.; Drexler, I.; Walotka, L.; Grothmann, R.; Ptok, J.; Hillebrandt, J.; Ritchie, A.; Rabl, D.; Ostermann, P. N.; Robitzsch, R.; Hauka, S.; Walker, A.; Menne, C.; Grutza, R.; Timm, J.; Adams, O.; Schaal, H.
title: Age-dependent immune response to the Biontech/Pfizer BNT162b2 COVID-19 vaccination
date: 2021-03-05
journal: nan
DOI: 10.1101/2021.03.03.21251066
sha: e3183bf897d83eeadf8e36f6c6a715c466e99c50
doc_id: 1025502
cord_uid: 9nyfz7s2

Background: The SARS-CoV-2 pandemic has led to the development of various vaccines. Real-life data on immune responses elicited in the most vulnerable group of vaccinees over 80 years old is still underrepresented despite the prioritization of the elderly in vaccination campaigns. Methods: We conducted a cohort study with two age groups, young vaccinees below the age of 60 and elderly vaccinees over the age of 80, to compare their antibody responses to the first and second dose of the BNT162b2 COVID-19 vaccination. Results: While the majority of participants in both groups produced specific IgG antibody titers against SARS-CoV-2 spike protein, titers were significantly lower in elderly participants. Although the increment of antibody levels after the second immunization was higher in elderly participants, the absolute mean titer of this group remained lower than the <60 group. After the second vaccination, 31.3 % of the elderly had no detectable neutralizing antibodies in contrast to the younger group, in which only 2.2% had no detectable neutralizing antibodies. Conclusion: Our data suggests that lower frequencies of neutralizing antibodies after BNT162b2 vaccination in the elderly population may require earlier revaccination to ensure strong immunity and protection against infection.

public health emergency of international concern. With limited drug treatment options 46 available, research on prophylactic immunization, especially for high-risk groups, became a priority [2] .

The zoonotic beta-coronavirus SARS-CoV-2 is closely related to severe acute CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 adults over 65 years of age account for approximately 80% of hospitalizations [6, 7] 60 and higher death rates have been reproducibly reported in this population [8, 9] .

Additionally, prolonged disease from hospitalization, delayed viral clearance, and/or a 62 higher fatality rate is also reported to be age-related [9] . Comorbidities such as 63 cardiovascular disease, diabetes, and obesity are discussed as the primary cause of 64 a more severe COVID-19 course, however, these comorbidities alone do not explain 65 why age is such a strong risk factor.

Aging is accompanied by changes in the immune system, particularly affecting 67 adaptive immunity's three fundamental pillars, i.e. B cells, CD4+ T cells, and CD8+ T 68 cells [10] . Although hallmarks of immunosenescence depend on multifaceted factors 69 and vary greatly between individuals, they are generally considered to be related to i) 70 the decreased ability to respond to new antigens associated with a reduced peripheral 71 plasmablast response; (ii) decreased capacity of memory T cells and (iii) a low level of 72 persistent chronic inflammation [11] [12] [13] [14] . This leads to declining immune efficiency and 73 fidelity, resulting in increased susceptibility to infectious diseases and decreased 74 response to vaccinations. Additionally, it contributes to increased susceptibility to age-75 related pathological conditions including cardiovascular diseases or autoreactive 76 diseases such as rheumatoid arthritis [12, 15] .

In December 2020, the first vaccines for COVID-19 were approved worldwide and the 78 first vaccinations were carried out [16] [17] [18] [19] . While the German Standing Committee on 79 Vaccination (STIKO) recommends immunization against SARS-CoV-2, access to the 80 vaccine in Germany and many other countries worldwide at the beginning of 2021 is 81 offered in a prioritization procedure due to limited availability. First, groups of people 82 who are at particularly high risk for severe courses of COVID-19 disease or who are 83 professionally in close contact with such vulnerable people were vaccinated. These 84 two prioritized groups include senior residents of nursing homes aged ≥ 80 years, and 85 their caregivers typically aged ≤ 65 years. A recent, thorough study using mathematical 86 modeling to investigate vaccine prioritization strategies supports the preferential 87 vaccination of the elderly [20] . This study describes a scenario where cumulative 88 incidence rates were minimized when vaccination of the population aged 20-49 years 89 was prioritized, while mortality was decreased when the population aged 60 years or 90 older was prioritized. This model took age-structure, age-related efficacy, and 91 infection-fatality rates into account. They conclude that prioritizing the population aged 92 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101/2021.03.03.21251066 doi: medRxiv preprint > 60 years, thus directly protecting the vulnerable population, would decrease mortality 93 rates, a strategy that is currently employed by various nations but without the support 94 of recent and thorough data [20] .

The current vaccination strategy for the Biontech/Pfizer Comirnaty (BNT162b2) is a 96 two-step "prime and boost" procedure in which the first vaccination is followed by a CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. Binding Antibody Units). The upper detection limit for undiluted samples was > 384 133 BAU/ml, the lower detection limit was < 3.2 BAU/ml. For samples over the detection CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101/2021.03.03.21251066 doi: medRxiv preprint

The data were analyzed using SPSS Statistics 25 (IBM © ) and GraphPad Prism 9.0.00 158 (GraphPad Software, San Diego, CA, USA). Categorical data were studied using

Fisher's exact test or Pearson's chi-square test, depending on the sample size. 

Three vaccines were tested positive and therefore were excluded from the dataset. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. Vaccination-induced SARS-CoV-2 spike specific IgG levels differ between young and 

The comparison of SARS-CoV-2 spike specific IgG titers showed an extremely 208 significant (p<0.001) difference between the two age groups, after both the first and and SARS-CoV-2 specific antibody titer after first vaccination (D) and second vaccination (E). 226

Results < 25.6 BAU/ml as negative (red area), ≥ 25.6 BAU/ml ≤ 35.6 BAU/ml as indeterminate 227

(orange), and > 35.6 BAU/ml were considered positive. For comparison of two groups either 228 two-tailed parametric unpaired t-tests or paired t-test were performed. Correlation was 229 analysed by simple linear regression. P-values < 0.05 were considered statistically significant. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101/2021.03.03.21251066 doi: medRxiv preprint We next determined the neutralization capacity in our cohort after the first and second 236 dose of vaccination. At 17-19 days after the first vaccination, the majority of 237 participants, regardless of their age, failed to display neutralizing antibody titers. In the 238 group of younger vaccines, 16.1 % displayed neutralizing antibodies with titers ranging 239 between 1:10 to 1:2560. In the group of elderly vaccinees, only 1.2 % had developed 240 neutralizing antibodies after the first vaccination (Figure 2A) .

After the second dose, a neutralization titer was attained by 97.8% of the younger 242 vaccinees. In the elderly group, 68.7% showed titers ranging from 1:10 to 1:320.

Remarkably, in 31.3% of the elderly vaccinees neutralizing antibodies were not 244 detectable after the second vaccination, and thus, were potentially without 245 seroprotection ( Figure 2B ). To assess differences in post-vaccination symptoms between the age groups and to 255 evaluate a potential correlation with antibody titers, medical questionnaires were 256 completed at the two collection time points.

After the first vaccination, half of the younger cohort (51.6%) reported no symptoms, 258 the remaining vaccinees recorded post-vaccination symptoms with a score ranging 259 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101 https://doi.org/10. /2021 between 1 and 4. In turn, 93.9 % of elderly vaccinees reported no symptoms; the 260 remaining 6.1% reported either one or two of the scored symptoms ( Figure 3A ).

After the second dose, only 25.8% of the younger vaccinees had no symptoms. While CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. ; https://doi.org/10.1101/2021.03.03.21251066 doi: medRxiv preprint induced SARS-CoV-2 spike specific IgG and SARS-CoV-2 neutralizing antibodies.

While the majority of both young and elderly vaccinees raised IgG responses after their 286 second vaccination, the induction of ELISA-IgG and in particular neutralizing antibody 287 levels were significantly lower in the elderly vaccinees.

The main differences between the two groups of vaccinated individuals are likely a 289 consequence of immunosenescence, which describes the phenomenon of reduced 290 adaptive immune responses e.g. antibody responses in the elderly [23] . It is well 291 described that elderly individuals not only have higher rates of morbidity due to 292 infection but also respond less to vaccination [24] [25] [26] , mainly due to a decline in cellular 293 as well as humoral immunity.

The notion that humoral vaccination responses are impaired with increasing age is well 295 depicted in our cohort, as the mean titer of SARS-CoV-2 spike specific IgG remains 296 2.8-fold lower after the second vaccination for the elderly group of vaccinees compared 297 to the younger cohort ( Figure 1B) . Additionally, a general intra-and inter-group trend 298 in negative correlation between age and IgG titer is visible after both vaccinations 299 ( Figure 1C/1D ). More importantly, a similar age-dependent trend can be seen for 300 SARS-CoV-2 specific neutralizing antibody titers: While neutralization antibody titers 301 were attained by 97.8% of the younger vaccinees, 31.3% of the elderly remained 302 without neutralization antibody titers after the second vaccination ( Figure 2B ).

The lack of neutralizing antibody responses in about one-third of the elderly group 304 raises the questions whether the effectiveness of vaccine-induced immune protection 305 may be transferred to this population without explicit testing. Especially since 306 neutralizing, antibody levels correlate with protection against many viruses including 307 SARS-CoV-2 in humans [27, 28] and recent data suggest that high neutralizing titers 308 are particularly important for protection against novel circulating SARS-CoV-2 variants 309 confering immune escape [29] [30] [31] .

Although it is well known that the response to primary vaccination is weaker in the 311 elderly [24, 32] , it is remarkable that this observation also expands to the younger CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 5, 2021. been adopted in several countries. These include a delay of the second vaccination, 318 as implemented by the UK or Israel, to allow for the initial primary vaccination to a 319 larger proportion of the population, a strategy which is controversially discussed [35, 

This study provides insight into age-dependent limitations of immune responses 343 elicited after the first and second dose of the BNT162b2 vaccine. By comparing similar-344 sized cohorts of vaccinees aged < 60 years and > 80 years, we found that more than 345 30% of elderly vaccinees did not attain neutralizing antibody responses after their 346 second vaccination. Nevertheless, recent studies show that even after the first 347 vaccination, severe courses of COVID-19 are attenuated. The elderly population is 348 prioritized by many vaccination schedules, despite the fact that this age group is 349 underrepresented in previous studies, and hence, there is still a lack of data concerning 350 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. 

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