key: cord-0761768-u8wxij14
authors: Ishmukhametov, A. A.; Siniugina, A. A.; Yagovkina, N. V.; Kuzubov, V. I.; Zakharov, K. A.; Volok, V. P.; Dodina, M. S.; Gmyl, L. V.; Korotina, N. A.; Theodorovich, R. D.; Ulitina, Y. I.; Tsaan, A. A.; Pomaskina, T. V.; Kalenskaya, A. V.; Solovjeva, I. V.; Tivanova, E. V.; Kondrasheva, L. Y.; Ploskireva, A. A.; Akimkin, V. G.; Subbotina, K. A.; Ignatyev, G. M.; Korduban, A. K.; Shustova, E. Y.; Bayurova, E. O.; Kondrashova, A. S.; Avdoshina, D. V.; Piniaeva, A. N.; Kovpak, A. A.; Antonova, L. P.; Rogova, Y. V.; Shishova, A. A.; Ivin, Y. Y.; Sotskova, S. E.; Chernov, K. A.; Ipatova, E. G.; Kordu,
title: Safety and immunogenicity of inactivated whole virion vaccine CoviVac against COVID-19: a multicenter, randomized, double-blind, placebo-controlled phase I/II clinical trial
date: 2022-02-09
journal: nan
DOI: 10.1101/2022.02.08.22270658
sha: 0aa283e5e9392886bb06bc776b1a6eea7309865a
doc_id: 761768
cord_uid: u8wxij14

We present the results of a randomized, double-blind, placebo-controlled, multi-center clinical trial of the tolerability, safety, and immunogenicity of the inactivated whole virion concentrated purified coronavirus vaccine CoviVac in adult volunteers aged 18-60. Safety of the vaccine was assessed in 398 volunteers who received two doses of the vaccine (n=298) or placebo (n=100). The studied vaccine has shown good tolerability and safety. No deaths, serious adverse events (AE), or other significant AE related to vaccination have been detected. The most common AE in vaccinated participants was pain at the injection site (p<0.05). Immunogenicity assessment was performed in 167 volunteers (122 vaccinated and 45 in Placebo Group) separately for the participants who were anti-SARS-CoV-2 nAB negative (69/122 in Vaccine Group and 28/45 in Placebo Group) or positive (53/122 in Vaccine Group and 17/45 in Placebo Group) at screening. At Day 42 after the first immunization the seroconversion rate in participants who were seronegative at screening was 86.9% with average the geometric mean neutralizing antibody (nAB) titer of 1:20. Statistically significant (p<0.05) increase of IFN-{gamma} production by peptide-stimulated T-cells was observed at Days 14 and 21 after the first immunization. In participants who were seropositive at screening but had nAB titers below 1:256 the rate of 4-fold increase in nAB levels was 85.2%, while in the participants with nAB titers >1:256 the rate of 4-fold increase in nAB levels was below 45%. For the participants who were seropositive at screening the second immunization did not lead to a significant increase in nAB titers. In conclusion, inactivated vaccine CoviVac has shown good tolerability and safety, with 86.9% seroconversion rates in participants, who were seronegative at screening. In participants who were seropositive at screening and had nAB titers below 1:256, a single immunization lead to a 4-fold increase in nAB levels in 85.2% cases.

The study is a randomized, double-blind, placebo-controlled, multi-center clinical trial of the 1 4 0 tolerability, safety, and immunogenicity (Clinical trials, phase I/II) of the inactivated whole virion 1 4 1 concentrated purified coronavirus vaccine CoviVac in adult volunteers aged 18-60. the vaccine and 50 with placebo) (Figure 1 ). Safety assessment was performed in Stages 1-3 and 1 4 7

immunogenicity assessment was performed in Stage 3. 1 4 8

The study included participants from 18 to 60 years of age at the time of enrolment. During screening 1 4 9

all participants were tested for SARS-CoV-2 infection by PCR in nasopharyngeal swabs. The 1 5 0 participants of Stages 1 and 2 were also screened at enrolment for anti-SARS-CoV-2 IgM and IgG 1 5 1 antibodies by ELISA. Individuals positive in either test were not included. The participants of Stage 3 1 5 2

were included regardless of their SARS-CoV-2 IgM and IgG status at enrolment. Persons with history 1 5 3

of SARS-CoV-1, SARS-CoV-2, or MERS infection, confirmed contact with COVID-19 patients, 1 5 4

previous severe allergic reactions, tuberculosis, cancer, mental or autoimmune diseases were also 1 5 5 not included. All participants were screened for eligibility on the basis of their health status, including 1 5 6 their medical history, vital signs, physical examination and laboratory test results, and were enrolled 1 5 7

after providing signed and dated informed consent forms. Details of the inclusion, non-inclusion and 1 5 8 exclusion criteria can be found in the study protocol (clinicaltrials.gov ID NCT05046548). . CC-BY 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. (which was not certified by peer review)

The copyright holder for this preprint this version posted February 9, 2022. ; Figure 1 . Study profile. Horizontal light grey lines represent the Stages of the study. Dotted lines 1 9 1 Safety assessment 1 9 2

AEs were monitored until Day 42-45 after the 1 st vaccination (Day 28-31 after the 2 nd vaccination). 1 9 3

The solicited local AEs were pain, indurations, hematomas, swelling, itching and hypersensitivity at 1 9 4 the injection site, and solicited systemic AEs were fever, fatigue or malaise, nervous system disorders 1 9 5

(headache, lightheadedness), musculoskeletal and connective tissue disorders (arthralgia, myalgia), 1 9 6 disorders of respiratory system and mediastinal organs (pain/sore throat, nasal congestion, 1 9 7 . CC-BY 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. (which was not certified by peer review)

The copyright holder for this preprint this version posted February 9, 2022. ; rhinorrhea, cough, shortness of breath), gastrointestinal tract disorders (nausea, vomiting, diarrhea, 1 9 8 impaired appetite). All unsolicited AEs were reported by participants throughout the study. 1 9 9

AEs were graded as mild, moderate or severe according to the severity scoring chart (Supplementary  2  0  0  Table 1) and assessed for the probability of their relation to the tested vaccine (highly  2  0  1 probable/certain, probable, possible, unlikely, unrelated, unknown). 2 0 2 2 0 3

Immunogenicity assessment 2 0 4

Humoral immunity against SARS-CoV-2 was assessed in serum samples using chemiluminescent 2 0 5 microparticle immunoassays (CMIA) and virus neutralization test (NT). 2 0 6

IgG antibodies to nucleocapsid protein (N) were detected using Architect SARS-CoV-2 IgG CMIA 2 0 7

(Abbott Diagnostics, USA). IgG antibodies to receptor-binding domain (RBD) of the spike protein (S) 2 0 8

were detected using Access SARS-CoV-2 IgG CMIA (Beckman, USA). 2 0 9

Serum samples from randomly selected participants were additionally tested in ELISA for total 2 1 0 antibodies against RBD with CoronaPass Total (Genetico, Russia) and for total antibodies to S 2 1 1 protein trimer (Vector-Best, Russia).

Neutralization test was performed using SARS-CoV-2 strain PIK35 in Vero cells as described were considered negative. Immunogenicity assessment was performed in 167 participants of Stage 3. 2 1 5

Interferon-gamma (IFN-γ) production in response to stimulation with SARS-CoV-2 S-protein peptides 2 1 6

was assessed using QuantiFERON SARS-CoV-2 Starter Set (Qiagen, Germany), using two SARS-2 1 7

CoV-2 S protein peptide pools (Ag1 and Ag2) designed to stimulate the production of IFN-γ by S-2 1 8

protein-specific CD4 (Ag1) and CD4/CD8 (Ag2) T cells, which was detected by ELISA according to 2 1 9 the manufacturer's protocol. A Mitogen tube served as positive control. The baseline IFN-γ level in the 2 2 0

Nil tube (unstimulated lymphocytes) was subtracted from the IFN-γ level in the antigen tubes and the 2 2 1

Mitogen tube to correct for background or non-specific IFN-γ signal. The results were reported in 2 2 2 international units of IFN-γ per milliliter of whole blood (IU/mL) using a dilution curve of the standard 2 2 3 supplied with the kit. Calibration curve was generated at each assay run. Samples were considered 2 2 4 reactive for an IFN-γ response if the IFN-γ levels obtained from the tubes with stimulus were 0.01 2 2 5 IU/mL above baseline levels obtained from the unstimulated control. The primary endpoints for safety assessment were the frequency and severity of AEs within the 2 2 9

observation period (72 h, 7 days after each vaccination and 28 days after the 2 nd vaccination). The 2 3 0 primary immunogenicity endpoints were the geometric mean nAB titer (GMT) and seroconversion rate 2 3 1

(the percentage of volunteers with 4-fold increase in GMT) 28 days after the 2 nd vaccination.

Secondary endpoints included seroconversion rates at Days 7 and 14 and Months 2, 3, 4, 5 and 6 2 3 3

after the 2 nd vaccination. . CC-BY 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 February 9, 2022. ;

The sample size was determined based on the requirements of the national guidelines, and the 2 3 7 distribution of the participants between Vaccine Group and Placebo Group was 3:1.

All parameters were evaluated using descriptive statistics (mean, standard deviation, percentile, 2 3 9 medians, min and max). All efficacy parameters are presented as mean with 95% confidence interval 2 4 0 (CI). Value comparisons (for example, GMT) were made using ANOVA or Mann-Whitney tests. P 2 4 1 values below 0.05 (two-sided) were considered to be significant. Frequencies (%) were compared 2 4 2

with Chi-square test or Fisher's exact test. Analysis of variance or Friedman's analysis were used for 2 4 3 comparisons of the parameters over time. Spearman's rank correlation coefficient was used for 2 4 4 correlation analysis. Study profile is presented in Figure 1 . Overall, starting from October 3, 2020, 498 volunteers were 2 4 9

screened for eligibility at three clinical sites. Based on clinical, laboratory and instrumental 2 5 0 examinations, 400 volunteers aged 18-60 years were enrolled in the study. All enrolled participants 2 5 1 were considered healthy and had no previous or current diagnosed comorbid conditions. All 2 5 2 participants were randomized by the sealed envelope method into 2 groups: 300 participants were 2 5 3 assigned to receive the vaccine and 100 participants were assigned to receive placebo (2 injections, 2 5 4 0.5 ml, 14 days interval for both the vaccine and placebo).

Two out of 300 participants from the Vaccine Group withdrew consent prior to administration of the 1 st 2 5 6

dose. Thus, safety assessment was performed in 398 (298 in the Vaccine Group and 100 in the 2 5 7

Placebo Group) participants of the study. Participants who contracted SARS-CoV-2 infection during 2 5 8 the observation period were not excluded from safety assessment. 2 5 9

Out of 200 (150 in the Vaccine Group and 50 in the Placebo Group) participants initially included into 2 6 0

Stage 3 for immunogenicity assessment, a total of 33 (28 from the Vaccine Group and 5 from the 2 6 1

Placebo Group) were excluded during the observation period as they contracted SARS-CoV-2 2 6 2 infection or withdrew consent. Thus, immunogenicity assessment was performed in 167 (122 in the 2 6 3

Vaccine Group and 45 in the Placebo Group) participants of Stage 3.

The demographic characteristics of the participants in the safety and immunogenicity assessment 2 6 5 populations were similar across treatment groups in terms of sex, age, and BMI (Table 1 ). The mean 2 6 6 age of the study participants was 33.1 and 33.5 years, the female/male proportion was 36.9/63.1 and 2 6 7 34/66, and mean body mass index (BMI) was 23.8 and 24 kg/m 2 for the Vaccine Group and the 2 6 8

Placebo Group, correspondingly. . CC-BY 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 February 9, 2022. ; after the 2 nd vaccination). The studied vaccine has shown good tolerability and safety. No deaths, 2 7 5

serious AEs, or other significant AEs related to vaccination have been reported. All observed severe 2 7 6 adverse events (SAEs) were classified as unlikely to be related or unrelated to the tested vaccine. 2 7 7

In total, during the study period, 244 AEs were recorded in 136 (34.2 %) participants, of which 189 2 7 8

AEs were observed in 105 (35.2%) of Vaccine Group participants, and 55 AEs in 31 (31%) of Placebo 2 7 9

Group participants (Table 2, Supplementary Table S2, Supplementary Table S3) .

The most common AE in Vaccine Group was pain at the injection site. It was registered in the 2 8 1

Placebo Group as well, but was significantly less common (P<0.05).

Changes in the parameters of clinical blood tests, biochemical blood tests and general urine analysis, 2 8 3 observed at different time points, in most cases were regarded as clinically insignificant and unrelated 2 8 4

to vaccination (Supplementary Table S2, Supplementary Table S3 ). Clinically significant deviations in 2 8 5 the parameters of creatine phosphokinase, ALT, AST, CRP and leukocytes were observed in both 2 8 6 groups and their frequencies did not differ between the study groups. No clinically significant 2 8 7 deviations in the parameters evaluated during physical examination, neurological status and ECG 2 8 8

were observed in both groups. 2 8 9

One participant (0.3%, 0.1-1.9 95% CI) from the Vaccine Group died at Day 29 of the observation 2 9 0 period as a result of acute circulatory disorder. Autopsy examination revealed signs of chronic mild 2 9 1 hepatitis, pre-existing stromal cardiosclerosis and dilated cardiomyopathy manifested by myocardial 2 9 2 . CC-BY 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 February 9, 2022. ; Itching at the injection site Mild 1 (1%, 0,2-5,4%) / 1 1 (1%, 0,2-5,4%) / 1 Fever Mild 11 (3,7%, 2,1-6,5%) / 12 5 (1,7%, 0,7-3,9%) / 5 6 (2%, 0,9-4,3%) / 7 2 (2%, 0,6-7,0%) / 2 2 (2%, 0,6-7,0%) / 2 -Moderate 2 (0,7%, 0,2-2,4%) / 2 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ---

Mild 4 (1,3%, 0,5-3,4%) / 10 1 (0,3%, 0,1-1,9%) / 1 3 (1%, 0,3-2,9%) / 9 2 (2%, 0,6-7,0%) / 3 -2 (2%, 0,6-7,0%) / 3

Severe 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---

Mild 19 (6,4%, 4,1-9,7%) / 22 7 (2,3%, 1,1-4,8%) / 7 12 (4%) / 15 7 (7%, 3,4-13,7%) / 7 2 (2%, 0,6-7,0%) / 2 5 (5%, 2,2-11,2%) / 5

Moderate 3 (1%, 0,3-2,9%) / 3 1 (0,3%, 0,1-1,9%) / 1 2 (0,7%, 0,2-2,4%) / 2

Increased leukocytes content Moderate 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ----

Positive SARS-CoV-2 PCR test Mild 17 (5,7%, 3,6-8,9%) / 17 7 (2,3%, 1,1-4,8%) / 7 10 (3,4%, 1,8-6,1%) / 10 6 (6%, 2,8-12,5%) / 6 2 (2%, 0,6-7,0%) / 2 4 (4%, 1,6-9,8%) / 4

Moderate 2 (0,7%, 0,2-2,4%) / 2 2 (0,7%, 0,2-2,4%) / 2 Increased creatine phosphokinase level 

Mild 22 (7,4%, 4,9-10,9%) / 22 15 (5%, 2,2-11,2%) / 15 7 (2,3%, 1,1-4,8%) / 7 3 (3%, 1,0-8,5%) / 3 2 (2%, 0,6-7,0%) / 2 1 (1%, 0,2-5,4%) / 1

Moderate 7 (2,3%, 1,1-4,8%) / 7 3 (1%, 0,3-2,9%) / 3 4 (1,3%, 0,5-3,4%) / 4

Severe 1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1

Mild 20 (6,7%, 4,4-10,1%) / 20 14 (4,7%, 2,8-7,7%) / 14 6 (2%, 0,9-4,3%) / 6 3 (3%, 1,0-8,5%) / 3 2 (2%, 0,6-7,0%) / 2 1 (1%, 0,2-5,4%) / 1

Moderate 5 (1,7%, 0,7-3,9%) / 5 2 (0,7%, 0,2-2,4%) / 2 3 (1%, 0,3-2,9%) / 3 ---Severe ---1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1 Candidiasis Mild 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---Other upper respiratory tract infections Mild 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ----Moderate 2 (0,7%, 0,2-2,4%) / 2 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ---

Mild 11 (3,7%, 2,1-6,5%) / 20 4 (1,3%, 0,5-3,4%) / 4 9 (3%, 1,6-5,6%) / 16 6 (6%, 2,8-12,5%) / 12 3 (3%, 1,0-8,5%) / 3 3 (3%, 1,0-8,5%) / 9

Headache Mild 11 (3,7%, 2,1-6,5%) / 19 4 (1,3%, 0,5-3,4%) / 4 8 (2,7%, 1,4-5,2%) / 15 6 (6%, 2,8-12,5%) / 12 3 (3%, 1,0-8,5%) / 3 3 (3%, 1,0-8,5%) / 9

Dizziness Mild 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---

Mild 4 (1,3%, 0,5-3,4%) / 6 2 (0,7%, 0,2-2,4%) / 3 2 (0,7%, 0,2-2,4%) / 3

Moderate 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 2 1 (1%, 0,2-5,4%) / 1 1 (1%, 0,2-5,4%) / 1 -Arthralgia Mild 2 (0,7%, 0,2-2,4%) / 2 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ---Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---Lumbar pain Moderate ---1 (1%, 0,2-5,4%) / 1 1 (1%, 0,2-5,4%) / 1 -Myalgia Mild 4 (1,3%, 0,5-3,4%) / 4 2 (0,7%, 0,2-2,4%) / 2 2 (0,7%, 0,2-2,4%) / 2 ---Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---

Mild 3 (1%, 0,3-2,9%) / 3 1 (0,3%, 0,1-1,9%) / 1 2 (0,7%, 0,2-2,4%) / 2 1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1

Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 .

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 February 9, 2022. Diarrhea Mild 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1 Pyrosis Mild 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ----Nausea Mild 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---

Mild 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 -

Mild 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 ---- 

Mild 1 (0,3%, 0,1-1,9%) / 1 1 (0,3%, 0,1-1,9%) / 1 -1 (1%, 0,2-5,4%) / 1 1 (1%, 0,2-5,4%) / 1 -

Mild 2 (0,7%, 0,2-2,4%) / 8 -2 (0,7%, 0,2-2,4%) / 8 1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1

Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 Impaired appetite Mild 2 (0,7%, 0,2-2,4%) / 8 -2 (0,7%, 0,2-2,4%) / 8 1 (1%, 0,2-5,4%) / 1 -1 (1%, 0,2-5,4%) / 1

Moderate 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 ---

Severe 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1

Death from acute circulatory disorder** Severe 1 (0,3%, 0,1-1,9%) / 1 -1 (0,3%, 0,1-1,9%) / 1 * Differences are statistically significant (P<0.05) 3 0 1 ** Relation to vaccination classified as unlikely by the treating physician 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 February 9, 2022.

Selection of the method of humoral immunity assessment 3 0 5

To determine the optimal method of anti-SARS-CoV-2 humoral immunogenicity assessment we 3 0 6 compared the neutralizing antibody (nAB) detection rates in NT with two commercial CMIA tests 3 0 7

commonly used for the screening of anti-N protein IgG (Architect SARS-CoV-2 IgG, Abbott 3 0 8

Diagnostics, USA) and anti-RBD IgG (Access SARS-CoV-2 IgG, Beckman, USA). We used NT and 3 0 9

both CMIA tests to analyze serum samples from all 167 participants (122 from the Vaccine Group and 3 1 0 45 from the Placebo Group) included in Stage 3, obtained at screening and at Days 7, 14, 21, 28 and 3 1 1 42 after the 1 st immunization ( Table 3 ). The analysis included both the participants who were anti- There was no significant correlation between seropositivity rates assessed by NT and CMIA at all time 3 1 5 points (Table 3) . Therefore, further in order to assess the sensitivity of commercial CMIA and ELISA tests, serum 3 2 2 samples from 27 randomly selected participants from the Vaccine Group in Stage 3 who were anti-3 2 3

SARS-CoV-2 nAB negative at screening were used to evaluate the correlation between the virus 3 2 4 neutralization titers in NT and the positivity coefficients in binding antibody detection assays. Two 3 2 5

abovementioned CMIA tests and two ELISA-based tests detecting total antibodies to S trimer 3 2 6 expressed in eukaryotic system and total antibodies to RBD (SARS-CoV-2-AB total-EIA-BEST, 3 2 7

Vector-Best, Russia and CoronaPass Total kit, Genetico, Russia, respectively) were used (Figure 2 ). 3 2 8

Both ELISA-based total antibody detection kits showed higher correlation of seropositivity rates and 3 2 9

positivity coefficients with the virus neutralization titers in NT than the CMIA tests. The Vector-Best 3 3 0 . CC-BY 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 February 9, 2022. ; ELISA kit was able to detect total antibodies to S trimer in 3/27 participants at Day 14 after the 3 3 1 immunization ( Figure 2B) , while virus-neutralizing antibodies in NT ( Figure 2A ) and total antibodies 3 3 2 RBD ( Figure 2C ) were detected only from Day 21. 3 3 3

The analysis of the individual test results showed that in the samples with detectable nAB levels w 3 3 4 could see a statistically significant increase in the positivity coefficients in CMIA kits compared w 3 3 5 the samples obtained at screening (Figure 3 A,D,E) , but the levels were below the "grey zon 3 3 6 indicating insufficient sensitivity of these tests. Thus, we did not find a strong correlation between t 3 3 7 results of NT and the results of CMIA and ELISA tests ( Figure 3E ), and only NT results were used 3 3 8 further calculations of seroconversion rates. 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 February 9, 2022. ; line -Mean, whiskers -SD. Blue area signifies a positive threshold (grey zone) for each test. Black 3 4 6 dots represent the results from sera samples from 6 randomly selected participants from Placebo 3 4 7

Group obtained in the same tests in parallel (with Vector-Best sera from 3 participants were tested). is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted February 9, 2022. ; IFN-γ production by S-protein-specific CD4 and CD4/CD8 T cells using two SARS-CoV-2 S protein antibody detection kits showed higher correlation of seropositivity rates with NT results. Based on 4 4 6 these observations, only NT results were used for further calculations of seroconversion rates. 4 4 7

In total, immunogenicity assessment was performed by NT in 167 volunteers (122 in Vaccine Group  4  4  8 and 45 in Placebo Group) separately for the participants who were anti-SARS-CoV-2 nAB negative 4 4 9

(69/122 in Vaccine Group and 28/45 in Placebo Group) or anti-SARS-CoV-2 nAB positive (53/122 in 4 5 0

Vaccine Group and 17/45 in Placebo Group) at screening. 4 5 1

At Day 42 after the 1 st immunization the seroconversion rate in participants who were seronegative at 4 5 2 screening was 86.9% with average the nAB GMT of 1:20. However, these nAB levels are above the Wang et al., 2020), which would require boosting immunizations in the long term. In this study we 4 5 8

show the results of CoviVac immunization in participants with pre-existing anti-SARS-CoV-2 CC-BY 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. (which was not certified by peer review)

The copyright holder for this preprint this version posted February 9, 2022. ; https://doi.org/10.1101/2022.02.08.22270658 doi: medRxiv preprint

Effect of 2 Inactivated SARS-CoV-2 Vaccines on Symptomatic COVID-19 Infection in Adults: A 4

Efficacy 4 9 3 and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

Anti-SARS-CoV-2 receptor-binding domain antibody evolution after mRNA 4 9 8 vaccination

peptide pools (Ag1 and Ag2, respectively). The data is summarized in Figure 4 . 3 9 4Compared to baseline levels, we observed a statistically significant (p<0.05) increase of IFN-γ 3 9 5 production by peptide-stimulated CD4+ cells of vaccinated participants at Days 14 and 21 after the 1 st 3 9 6immunization and a statistically significant increase of combined IFN-γ production by stimulated CD4+ 3 9 7and CD8+ cells at Day 21 after the 2nd immunization, indicating the development of both SARS-CoV-3 9 8 2 S protein-specific CD4 helper and CD8 cytotoxic cells. Here we present the results of a randomized, double-blind, placebo-controlled, multi-center clinical 4 1 8trial of the tolerability, safety, and immunogenicity of the inactivated whole virion concentrated purified 4 1 9coronavirus vaccine CoviVac in adult volunteers aged 18-60.Overall, starting from October 3, 2020, 498 volunteers were screened for eligibility at three clinical 4 2 1 sites and 400 volunteers aged 18-60 years were enrolled in the study. All participants were 4 2 2 randomized into 2 groups: 300 participants were assigned to receive the vaccine and 100 participants 4 2 3were assigned to receive placebo (2 injections, 0.5 ml, 14 days interval for both the vaccine and 4 2 4 placebo). 4 2 5The studied vaccine has shown good tolerability and safety. No deaths, serious adverse events, or 4 2 6 other significant AEs related to vaccination have been reported. The most common AE in the Vaccine 4 2 7Group was pain at the injection site. It was registered in the Placebo Group as well, but was 4 2 8significantly less common (P<0.05). One participant (0.3%, 0.1-1.9 95% CI) from the Vaccine Group 4 2 9died at Day 29 of the observation period as a result of acute circulatory disorder, which was not 4 3 0 related to the tested vaccine. Autopsy examination revealed signs of chronic mild hepatitis, pre-4 3 1 existing stromal cardiosclerosis and dilated cardiomyopathy manifested by myocardial hypertrophy, 4 3 2 which were undetectable by the methods used at pre-vaccination screening. 4 3 3For immunogenicity screening we first assessed the sensitivity of two CMIA used for the detection of 4 3 4anti-SARS-CoV-2 IgG to N and S proteins and two ELISA kits widely used in the diagnostics of 4 3 5 SARS-CoV-2 infection, to estimate if their sensitivity is sufficient to detect the post-vaccination 4 3 6antibodies. There was no significant correlation between seropositivity rates assessed by 4 3 7neutralization test (NT) and CMIA (Table 3) , although we could see a statistically significant increase 4 3 8in the positivity indices in vaccinated participants who were seronegative at screening. This technically, nABs can belong to other classes. As compared to CMIA tests, both ELISA-based 4 4 5 5 9antibodies. 4 6 0In this study 'seroconversion' for the participants who were seropositive at screening was defined as 4 6 1 4-fold increase in nAB titers compared to baseline. The seroconversion rate for the participants who 4 6 2 had NT titers in NT below 1:256 at screening was comparable to that for participants who were 4 6 3 seronegative at screening (85.2% and 86.9%, respectively), while in the participants with nAB titers 4 6 4 >1:256 the seroconversion rate did not exceed 45%. For the participants who were seropositive at 4 6 5screening the 2nd immunization did not lead to a further significant increase in NT titers. Both facts 4 6 6 signify that there is a maximum level of antibodies against SARS-CoV-2, which human immune 4 6 7 system can produce, and further antigen addition is useless.The cellular immune response was assessed based on the production of IFN-γ by the CD4+ and 4 6 9 CD8+ lymphocytes after stimulation with SARS-CoV-2 S-protein peptide pools. Compared to baseline 4 7 0 levels, we observed a statistically significant (p<0.05) increase of IFN-γ production by peptide-4 7 1 stimulated CD4+ cells in vaccinated participants at Days 14 and 21 after the 1 st immunization and a 4 7 2 statistically significant increase of combined IFN-γ production by stimulated CD4+ and CD8+ cells at 4 7 3Day 21 after the 2nd immunization. 4 7 4In conclusion, inactivated vaccine CoviVac has shown good tolerability and safety, with 86.9% NT 4 7 5 seroconversion rates in participants, who were seronegative at screening. In participants who were 4 7 6 seropositive at screening and had nAB titers below 1:256, a single immunization lead to a 4-fold 4 7 7increase in nAB levels in 85.2% cases. These findings indicate that CoviVac can be successfully used 4 7 8both for primary immunization in two-dose regimen and for booster immunization as a single dose in 4 7 9individuals with reduced neutralizing antibody levels.