Longitudinal neutralization activities on authentic Omicron variant provided by three doses of BBIBP‐CorV vaccination during one year

Abstract

The majority of people in China have been immunized with the inactivated viral vaccine BBIBP‐CorV. The emergence of the Omicron variant raised the concerns about protection efficacy of the inactivated viral vaccine in China. However, longitudinal neutralization data describing protection efficacy against Omicron variant is still lacking. Here we present one‐year longitudinal neutralization data of BBIBP‐CorV on authentic Omicron, Delta, and wild‐type strains using 224 sera collected from 14 volunteers who have finished three doses BBIBP‐CorV. The sera were also subjected for monitoring the SARS‐CoV‐2 specific IgG, IgA, and IgM responses on protein and peptide microarrays. The neutralization titers showed different protection efficacies against the three strains. By incorporating IgG and IgA signals of proteins and Spike protein derived peptide on microarray, panels as potential surrogate biomarkers for rapid estimation of neutralization titers were established. These data support the necessity of the 3^rd dose of BBIBP‐CorV vaccination. After further validation and assay development, the panels could be used for reliable, convenient and fast evaluation of the efficacy of vaccination.

Abbreviations

pVNT

pseudovirus virus neutralization test

S protein

spike protein

ACE2

angiotensin‐converting enzyme 2

NT50

half‐maximal neutralizing titer

PFU

plaque forming unit

1. INTRODUCTION

COVID‐19 epidemic has swept the world for more than two years since it was first discovered at the end of 2019 [1, 2]. By July 26, 2022, there are 571.2 million cases and 6.3 million deaths of COVID‐19 (https://coronavirus.jhu.edu/map.html) [3]. The causative agent of COVID‐19 is severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), which is a single strand RNA virus [4]. Among the structural proteins, the spike protein mediates the entry of SARS‐CoV‐2 through attachment to ACE2 [5, 6, 7]. The mutant strains of SARS‐CoV‐2, like Delta variant and Omicron variant, have caused the epidemic rebound [8, 9, 10, 11] (https://www.who.int/en/activities/tracking‐SARS‐CoV‐2‐variants/). The Delta variant (B.1.617.2) quickly spread since 2021, which contains diverse mutation that increase immune evasion potential [12, 13, 14]. However, it was rapidly replaced by the Omicron variant. The Omicron variant (B.1.1.529.1) accumulates more than 30 mutations in its spike protein, and there are at least 15 mutations in the receptor binding domain, which leads significant escape from neutralization of existing neutralization antibodies [15].

To reduce morbidity and mortality, an efficacious vaccine is essential. In the past two years, fast development of SARS‐CoV‐2 vaccines has played a key role in the reduction of SARS‐CoV‐2 infections and COVID‐19 severity (from severe to mild disease) [16]. The FDA has approved 37 vaccines for emergency use as of April 21, 2022, (https://covid19.trackvaccines.org/). These vaccines can be broadly classified as nucleic acid‐based platform [17, 18], virial vector‐based platform [19, 20], recombinant protein subunit, and virus‐based platform [21]. Among them, the inactivated viral vaccine has a well‐established preparation process and high safety, besides, exposure of the whole viral particle to the immunity system can elicit neutralization antibodies targeted more than single antigen [22, 23]. The clinical data from China and other countries revealed the good protection efficacy of BBIBP‐CorV and CoronaVac, either with two doses or plus the booster dose [24, 25, 26, 27].

The emergence of SARS‐CoV‐2 mutants raised concerns about the level of vaccine efficacy reduction against the mutants, especially the Omicron variant. Recent studies revealed that, in comparison to the WT strain, the resistance of the vaccine to the Omicron variant decreased significantly as demonstrated by pVNT assay [26] and other immunoassay [28, 29], however, the neutralization of authentic Omicron variant for BBIBP‐CorV, especially, after the booster dose has not been reported yet. The neutralization assay of the authentic virus is the gold standard to evaluate the efficacy of vaccine, however, the assay needs to be performed in biosafety level 3 (BL‐3) facility, the operation is tedious and time‐consuming. Previously, we established the SARS‐CoV‐2 proteome microarray which contains 21 proteins of SARS‐CoV‐2 [30 _, 31], the Spike protein derived peptide microarray [32, 33], and the microarray with mutant RBDs [34]. Taking advantage of these microarrays, we have set up the correlation between the protein/peptide signals of microarray and neutralization titers (NT₅₀) and established a panel that could potentially serve as surrogate biomarker for evaluating vaccine efficacy against the WT SARS‐CoV‐2 [35]. Thus, while obtaining the values of NT₅₀ of antibodies against the Omicron variant elicited by BBIBP‐CorV, is it possible that the SARS‐CoV‐2 proteins and Spike protein derived peptides could also be used to establish a similar evaluation system for the Omicron variant?

Significance of the study

There are clear evidences that the mutations in the spike protein leads to significant escape from existing neutralization antibodies. Previous studies have demonstrated that the vaccine triggered neutralization activity to the Omicron variant decreased significantly by pVNT assays and other immunoassays. In this study, we analyzed the protection efficacy of BBIPB‐CorV against authentic SARS‐CoV‐2 mutants and revealed the level of neuralization activity at different time point. To our knowledge, this is the first systematical neutralization data covering the whole vaccination process of BBIBP‐CorV. Using a microarray approach, we profiled IgG, IgA, and IgM responses of the year‐long longitudinal serum samples, we also showed the dynamic change of antibody response to both SARS‐CoV‐2 proteins and S protein derived peptides after three doses of BBIBP‐CorV. In addition, combination of proteins and peptides of IgG and IgA channels can predict the protection efficacy of BBIBP‐CorV against the Omicron variant. The results from this study support the necessity of the 3rd dose of BBIBP‐CorV vaccination. The panels of surrogate biomarkers have considerable translational potential, after further validation and assay development, they could be applied for reliable, convenient and fast evaluation of the efficacy of BBIBP‐CorV vaccination.

Herein, we recruited 14 volunteers who have been vaccinated with three doses of BBIBP‐CorV in 2021, and sampled longitudinal sera before the 1st dose till one month after the 3rd dose. The sera were tested for NT₅₀ on authentic viruses and IgG, IgA, and IgM responses on microarrays. We revealed the dynamic trend of the IgG, IgA, and IgM responses triggered by BBIBP‐CorV, observed significant higher neutralization activity after the 3rd dose, and established panels as potential surrogate biomarkers for rapid and accurate evaluation of NT_50.

2. MATERIALS AND METHODS

2.1. Participants and samples

A total of 14 volunteers were enrolled in this study. Participants of vaccination were recruited from January 2021, the participants were vaccinated with the inactivated virus vaccine BBIBP‐CorV, and collected longitudinal sera samples at 16 time points for one year (From Jan 6th, 2021 to Dec 24th, 2021), the samples collected before vaccination could serve as negative or blank controls, which was named as “Time point 1”, after 7 days of the first dose, serum samples were collected for the second time (Time point 2), after 7 days of the second dose, serum samples were collected for the third time (Time point 3), there were 7 days between Time point 3 and 4. After that, serum samples were collected once per month. After collecting samples at time point 13, the participants were vaccinated with the booster dose, and the serum samples were collected after 7 days (Time point 14), 14 days (Time point 15), and 30 days (Time point 16). (Figure 1). No breakthrough infection of SARS‐CoV‐2 was reported for all the volunteers during the one‐year vaccination process, and the characteristics of the 14 participants were shown in Table 1.

FIGURE 1.

Schematic diagram and workflow. A total of 14 healthy donors immunized with three doses of the inactivated virus vaccine BBIBP‐CorV were involved in this study. Longitudinal serum samples were collected for each donor at 16 time points through a whole year, including before the 1st dose, after the 1st dose, the 2nd dose and the 3rd (booster) dose. The samples were then subjected to SARS‐CoV‐2 protein/peptide microarray analysis for IgG, IgA, and IgM responses simultaneously, and also applied to neutralization assay (plaque reduction neutralization test, PRNT) against authentic SARS‐CoV‐2 viruses, that is, the WT strain, the Delta variant, and the Omicron variant. The sera used in the Omicron variant neutralization assay were collected at time points 3, 4, 14, 15, and 16. The microarray signals were correlated to the neutralization titers, through multi‐factor linear equations fitting, a model was established to predict the NT50 of authentic virus neutralization assay through the microarray signals of a combination of proteins and peptides. This model could serve as a potential surrogate biomarker for evaluating the vaccine efficacy for each individual at any time point.

TABLE 1.

Characteristics of the 14 participants

Characteristics of the vaccinated cohort
Numbers		14
Age		40.2 ± 7.9
Gender	Male	11
	Female	3
Source		Shanghai Jiao Tong University, Shanghai

2.2. Protein and peptide microarray fabrication

The N‐terminal amidated peptides were synthesized by GL Biochem, Ltd. (Shanghai, China). According to the manufacturer's instructions, each peptide was individually conjugated with BSA using Sulfo‐SMCC (Thermo Fisher Scientific, MA, USA). Briefly, BSA was activated by Sulfo‐SMCC in a molar ratio of 1:30, followed by dialysis in PBS buffer. Peptides containing cysteine were added in a w/w ratio of 1:1 and incubated for 2 h, followed by dialysis in PBS to remove free peptides. The peptide‐BSA conjugates, RBD proteins (Acro Biosystem, Beijing, China), S protein and S1 protein (Abclonal, Wuhan, China) of SARS‐CoV‐2, along with the negative (BSA) and positive controls (Human IgG and IgM), were printed in three replicates on PATH substrate slide (Grace Bio‐Labs, Oregon, USA) to generate identical arrays in a 2 × 7 subarray format using Super Marathon printer (Arrayjet, UK). The microarrays were stored at ‐80°C until use.

2.3. Microarray‐based serum analysis

A 14‐chamber rubber gasket was mounted onto each slide to create individual chambers for the 14 identical subarrays. The microarray was used for serum profiling as described previously with minor modifications [31, 32]. Briefly, the arrays were brought from ‐80°C to ‐20°C and room temperature for gradient rewarming and then incubated in blocking buffer (3% BSA in 1×PBS buffer with 0.1% Tween 20) for 3 h. A total of 200 μL of diluted sera was incubated with each subarray overnight at 4°C. The sera were diluted at 1:200. The microarrays were washed with 1×PBST and the bound antibodies were detected by incubating with Cy3‐conjugated goat anti‐human IgG, Alexa Fluor 647‐conjugated donkey anti‐human IgM and Alexa Fluor 488‐conjugated goat anti‐human IgA (Jackson ImmunoResearch, PA, USA), which were diluted for 1:1000 in 1×PBST. The incubation was carried out at room temperature for 1 h. The microarrays were then washed with 1×PBST and dried by centrifugation at room temperature and scanned by LuxScan 10K‐A (CapitalBio Corporation, Beijing, China) with the parameters set as 95% laser power/ PMT 500, 95% laser power/ PMT 550, for IgG and IgM. IgA was scanned by GenePix4200A (Molecular Devices, California, USA) with the parameters set as 95% laser power/ PMT 300. The fluorescent intensity was extracted by GenePix Pro 6.0 software (Molecular Devices, CA, USA).

2.4. Neutralization assay of the authentic virus

A plaque reduction neutralization test was performed to detect the NT50 of serum samples. Vero‐E6 cells were grown at 37 °C and 5% CO₂ for 15 h, and 150 μL serial dilutions of sera from volunteers were mixed with an equal volume of authentic SARS‐CoV‐2 virus (240 to 400 PFU/mL) and incubated at 37°C for 1 h. Next, 250 μL serum–virus mixture was added to Vero‐E6 cells. After incubation at 37°C for 1 h, the culture medium of the serum–virus mixture was replaced with 2.5% FBS‐DMEM containing 0.9% carboxymethylcellulose, and the mixture was further incubated at 37°C and 5% CO₂ for 3 to 4 days. The cells were then fixed with 8% paraformaldehyde and stained with 0.5% crystal violet. Each dilution group was replicated for three times. Plaques were counted, the inhibition rate was calculated, and the NT50 was determined by normalized response logistic regression analysis using GraphPad Prism 7.0.

2.5. Statistical analysis

For protein and peptide microarray, signal intensity of each spot was defined as the median of the ground subtracted by the median _background. The signal intensities of the three replicates spots for each peptide or protein were averaged. IgG, IgM, and IgA data were analyzed separately. p‐values for statistical analysis were calculated by Mann‐Whiney U test. All diagram and statistical analyses were carried out using GraphPad Prism 7.0 software and SPSS 24.0 software. Correlations were calculated using the R package.

3. RESULTS

3.1. The schematic and the study design

To evaluate the vaccine protection efficacy against the Omicron variant, and to monitor the levels of efficacy against the Omicron variant at different time points, we used a longitudinal sera cohort as described previously [34]. Briefly, 14 volunteers immunized with three doses of BBIBP‐CorV were involved, longitudinal sera were collected from these volunteers at 16 time points, that is, start prior to the 1st dose till one month after the 3rd dose (Figure 1). The sera were aliquoted and subjected to neutralization assay on authentic viruses, that is, the Omicron variant, the Delta variant and the WT strain. Meanwhile, the sera were also analyzed on protein and peptide microarrays to profile the SARS‐CoV‐2 specific antibody responses, that is, IgG, IgA, and IgM, simultaneously. The microarray results were then correlated to the neutralization assays of the authentic viruses, models were generated for estimating the neutralization activity of the Omicron variant from antibody responses.

3.2. Longitudinal sera neutralization assays for the Omicron variant reveals a significant increase of neutralization activity after the 3rd dose of vaccination

To assess the neutralization activity, the authentic virus neutralization assay was performed for four serum titers (20:1, 80:1, 320:1, and 1280:1), the results were applied to fit the NT₅₀ for the three strains (Figure S1A). Because of the very weak SARS‐CoV‐2 specific antibody levels 6 months after the 2nd dose of vaccination [34], sera collected from time point 10 to 13 were not tested against the WT strain and the Delta variant. To further save the valuable resource of the biosafety facility, sera collect at only five time points, that is, 3, 4, 14, 15, and 16, which represent relatively high antibody level after the 2nd dose and the 3 dose, were tested for the authentic Omicron variant. No positive signal was observed for unvaccinated samples both on the microarray and in the authentic virus neutralization assays. It is clear that the NT₅₀ for both the WT strain and the Delta variant were increased significantly after the 2nd dose in average, and reached the peak in the second week after the 2nd dose, then decreased gradually. After the 3rd dose, it was raised more significantly than that of the 2nd dose, and also decreased after the plateau of the second week (Figure 2A).

FIGURE 2.

Authentic SARS‐CoV‐2 virus neutralization assays with longitudinal sera collected from BBIBP‐CorV vaccinated donors. (A) The dynamic change of neutralization titers of all the donors in average (n = 14). (B) Comparison of neutralization titers among the three strains at time points 3, 4, 14, 15, and 16. (C) Comparison of neutralization titers of the Omicron variant among time points 3, 4, 14, 15, and 16. (D) Comparison of neutralization titers between the highest point of the WT strain after the 2nd dose and the highest points of the Omicron variant after the 3rd dose. (E) Comparison of neutralization titers between the highest point of the Delta variant after the 2nd dose and the highest points of the Omicron variant after the 3^rd dose. (F‐G) Correlations between IgG signal of RBD and NT₅₀ for the WT strain (F) and the Omicron variant (G), respectively. The p values were calculated by the Mann‐Whiney U test, p value: *<0.05, **<0.01, ***<0.005, ****<0.001, ns represents not significant. See also Figure S1‐5.

For some donors, the trends of NT₅₀ varied and are not consistent to the average (Figure 2A), which may due to individual differences of the immune system (Figure S1B‐1O). The two variants had different extent in NT₅₀ decrease as compared to that of the WT strain. At the time point of 3 and 4, the NT₅₀ for WT strain were 16.04× and 26.83× folds to that of the Omicron variant, and 9.03×, 10.94×, and 7.69× folds for time points 14, 15, and 16, respectively (Figure 2B). The reduction of NT₅₀ for Delta variant was not as significant as that of Omicron variant, the average NT₅₀ for WT strain at the 5 time points were 1.83×, 2.66×, 2.26×, 1.41×, and 1.48× compared to that of the Delta variant, respectively (Figure 2B). Currently, one of the most interesting questions of COVID‐19 vaccine is what extent of protection that the 3rd dose can provide against the Omicron variant. The NT₅₀ for Omicron variant showed a similar trend, the NT₅₀ at time point 14 was the highest, and was 11.21x as that of time point of 4 (Figure 2C). After the booster dose, we found that the highest NT₅₀ for the Omicron variant is 41.7% to the highest NT₅₀ for the WT strain after the 2nd dose, while the highest NT₅₀ for the Omicron variant was comparable to the highest NT₅₀ of the Delta variant after the 2nd dose (Figure 2D and 2E). The neutralization assays of authentic viruses indicated that the inactivated viral vaccine protection efficacy against the Omicron variant is generally weaker than that the WT strain and the Delta variant, fortunately, the 3rd dose can provide much higher protection efficacy against the Omicron variant as compared to the 2nd dose.

According to previous studies, the neutralization activity against authentic SARS‐CoV‐2 has high correlation with RBD‐specific IgG response[35]. Herein, we further explored the correlation between NT₅₀ of the three strains and IgG, IgA, IgM responses of S, S1, and RBD signals on microarrays (Figure S2), as well as a microarray with RBD of the Omicron variant [34]. The Pearson's coefficient between RBD‐specific IgG response and NT₅₀ was ∼ 0.80 for WT strain (Figure 2F) and ∼ 0.44 for RBD of the Omicron variant (Figure 2G). The Pearson's coefficient between S protein‐specific IgG response were ∼ 0.78, 0.70, and 0.64 for the WT strain, the Delta variant, and the Omicron variant, respectively. For S1 protein‐specific IgG response, the coefficient was slightly lower than that of RBD and S protein but still positively correlated with NT₅₀ (Figure S3). The IgA response showed similar results as IgG (Figure S4) and weaker correlations were observed for IgM response (Figure S5). These results indicate that the IgG and IgA responses to individual proteins could represent the NT₅₀ of the authentic Omicron variant to some extent.

3.3. The SARS‐CoV‐2 specific antibody responses at peptide level and the identification of protein/peptide panel for efficacy evaluation

To establish a panel of surrogate biomarker for rapid evaluation of the vaccine protection efficacy against SARS‐CoV‐2, we had developed a series of protein/peptide combinations at IgG level for predicting the NT₅₀ against the WT SARS‐CoV‐2 strain [35]. Currently, the most prevalent strain is the Omicron variant, and thanks to the restricted regulations and the “zero” policy, there is very few domestic COVID‐19 cases reported in China in 2021 when we were collecting the samples. Thus, it is highly possible that there was no breakthrough infection in our cohort. It is of great interest that the correlation between the neutralizing titer and the antibody response against the peptides can be used to evaluate the protection efficacy against the Omicron variant that was provided by the vaccination. To address this need, we performed serum incubation on a microarray with S protein derived peptides [32] (Figure S2B), analyzed the correlation between NT₅₀ against the Omicron variant and each peptide. At IgG level, a number of peptides showed high correlations, for example, 0.73 for S2‐78, and >0.6 for S2‐55, S1‐105, S1‐106, S1‐97, and S1‐37. At IgA level, there were also peptides with high correlation, such as S1‐57 (∼ 0.67) (Figure 3A). We chose the peptides with correlation coefficient beyond 0.6 at IgG level and peptides with correlation coefficient beyond 0.5 at IgA level for further analysis.

FIGURE 3.

IgG and IgA responses to S protein derives peptides for Omicron variant. (A) Correlation ecoefficiencies between the microarray signals (IgG and IgA) of all peptides and the NT₅₀. (B) Multi‐factor linear equations fitting for combination of proteins and peptides.

To set up the correlation between the microarray signal and NT₅₀ of the authentic Omicron variant, we performed multi‐factor linear equation fitting using the peptides and S, S1, RBD of WT strain, the IgG and IgA signal of Omicron RBD [34] (RBD_O) from the previous study [35] were also included in the calculation. Finally, we found the combination of S2‐78, S2‐55, S1‐105, S1‐106, S1‐37, S1, S, and RBD_O at IgG level can fit well with the NT₅₀, and combination of S1‐57, RBD_O, RBD at IgA level can fit well with the NT₅₀. Besides, we performed the calculation by including both the IgG and the IgA signal, as the result, the best combination, that is, S2‐78, S2‐55, S1‐106, S1‐37, S, RBD_O, A_S2‐53, A_S1‐33, A_RBD, A_RBD_O (“A_” represents IgA) reaches a high correlation of 0.9676 to the NT₅₀ of the authentic Omicron variant (Figure 3B). Furthermore, we also performed the same calculation for Delta variant and the wild type strain. The combination of S2‐39, S1‐106, S2‐19, S, AS1‐35, AS2‐39, AS1‐106, AS, AS1 (“A_” represents IgA) reaches a high correlation of 0.9405 to the NT₅₀ of the authentic Delta variant (Figure. 4B), and combination of S1‐31, S1‐50, S1‐78, AS2‐44, ARBD, S1, RBD (“A_” represents IgA) reaches a high correlation of 0.9727 to the NT₅₀ of the authentic SARS‐CoV‐2 wild type strain (Figure. 5B). After further validation and assay development, the combinations may could be used for reliable, convenient and fast evaluation of the efficacy of vaccination.

FIGURE 4.

IgG and IgA responses to S protein derives peptides for Delta variant. (A) Correlation ecoefficiencies between the microarray signals (IgG and IgA) of all peptides and the NT₅₀. (B) Multi‐factor linear equations fitting for combination of proteins and peptides.

FIGURE 5.

IgG and IgA responses to S protein derives peptides for wild type strain. (A) Correlation ecoefficiencies between the microarray signals (IgG and IgA) of all peptides and the NT₅₀. (B) Multi‐factor linear equations fitting for combination of proteins and peptides.

4. DISCUSSION

The emergence of Omicron variant lead to the new round of epidemic spread around the world. With the wide‐spreading of SARS‐CoV‐2 infection, there are several types of Omicron sublineage [36], among them, Omicron sublineages BA.2.12.1, BA.4, and BA.5 have higher transmissibility than the BA.2 lineage [37]. The neutralization study for BA.4 and BA.5 sublineages showed reduced neutralization activity from individuals vaccinated with three doses of Pfizer or AstraZeneca vaccine as compared to that of BA.1 and BA.2 [38]. For BBIBP‐CorV protection efficacy against the Omicron variant, there is still lack of neutralization data with authentic virus during the 3‐dose vaccination program. We collected sera from volunteers who have been immunized with three doses of BBIBP‐CorV, and tested neutralization activity to evaluate the protection efficacy provided by the neutralization antibodies during the whole vaccination progress. The negative controls were sera collected before the 1st dose from the same group of donors (Time point 1 in Figure 1A), which could be used as background controls for vaccination triggered SARS‐CoV‐2 specific humoral immunity, thus reduces the person‐to‐person variation when recruiting other unvaccinated people as controls. The dynamic change in neutralization activity against the WT strain, the Delta variant and the Omicron variant at different time points reveals that the extend of vaccine efficacy against the Omicron variant is weaker than that of the Delta variant and the WT strain, while the booster dose could significantly strengthen the protective efficacy against the Omicron variant.

Because of the significant role of the Spike protein (S, S1, and RBD), based on the microarray results, we also analyzed the dynamic trends of the IgG, IgM, and IgA responses. In humoral response, IgM plays key role in the primary immunization [39], and the secondary immunization is usually associated with IgG and IgA. The S‐, S1‐, and RBD‐specific IgM responses showed that the signal increased after the 1st dose, reached the peak after the 2nd dose, and then decreased gradually. The booster dose can stimulate a slightly higher IgM response, but lower than the peak after the 2nd dose (Figure S2D), this is consistent with the common knowledge of IgM response. IgA has a key role in mucosal immunity against SARS‐CoV‐2 infection [40]. Our results demonstrate that IgA is generally correlated with IgG (Figure S2E). Furthermore, the correlation analysis between the IgA response and NT₅₀ of the authentic Omicron variant showed a similar highly correlation as that of IgG, which is consistent with existing research [41].

As the key domain that mediate viral entry, RBD specific antibody neutralization was extensively studied, high plasma or serum RBD binding activity was observed. For the Omicron variant, there are more than 15 mutations on RBD, which cause significant escape of neutralization by antibodies [15], and reduce the protection efficacy of the vaccines that were developed based on the WT strain. Focused on RBD, we analyzed the correlation between the antibody responses against RBD of the Omicron variant and the corresponding NT₅₀ on authentic virus. Compared with RBD of the WT strain, the correlation coefficient between RBD_O and the corresponding NT₅₀ was ∼ 0.44 (Figure 2G), while the correlation coefficient between RBD of WT strain and NT₅₀ of Omicron variant was ∼ 0.64 (Figure S3G), this inconsistency may due to the immunogen of BBIBP‐CorV is the WT SARS‐CoV‐2, the neutralizing antibodies elicited by this vaccine are generally against the WT strain, not the Omicron variant.

According to our results, it is clear that IgA responses could also be used as potential surrogate biomarkers for estimating the protection efficacy of BBIBP‐CorV. There are abundant IgAs in the mouth and nose [42], including SARS‐CoV‐2 specific IgAs [43], and it is known the level of IgA in blood is highly correlated to that in the mouse and nose [44]. It will be interesting to check the SARS‐CoV‐2 specific IgAs by testing saliva, nasal swab or throat swab, correlate them with the neutralization assays of authentic Omicron variant, and setup a new IgA based surrogate biomarker panel similar to that of the serum‐based IgA panel. Because of the noninvasive manner for collecting saliva, nasal swab or throat swab, this will further simplify the final assay for assessing the IgA based protection efficacy that provided by BBIBP‐CorV.

Our research has some limitations. Firstly, the cohort lacks volunteers over 60 year‐old, the data of the 3^rd dose for these people may bring greater guiding significance to the vaccination for the elderly. Secondly, the Omicron strain prevalent in China was BA.2 when the study was carried out, however, the strain used in the neutralization assay was BA.1. The difference in escape immunity between BA.1 and BA.2 is low, so the study of BA.1 could represent BA.2 to a fair extent [45]. In this study, we have selected several peptides to establish the evaluation system of vaccine efficacy, among them, there is only one peptide related to a mutation location (S1‐57 PFGEVFNATRFA, which is PFDEVFNATRFA in Omicron BA.1 variant). Thus, we expect that the selected peptides are suitable for the variants. In fact, there is no doubt that more variants will appear in the near future due to the wide‐spread infection, it is possible that some of the peptides used for the antibody assay may not be up‐to‐date for the novel variants. Finally, the size of the cohort is small, though what we tested were longitudinal samples, which could theoretically reduce a large portion of the person‐to‐person variation. We think a larger cohort could certainly strengthen our findings.

In summary, to our knowledge, we provided the first systematical neutralization data during the whole vaccination process of BBIBP‐CorV, that is, two doses plus the booster dose. These data clearly support the necessity of the booster dose. After further validation and assay development, we anticipate the surrogate biomarker panels be applied for rapid evaluating the protection efficacy against Omicron variant, which may enable personalized and precise vaccination.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

ETHICAL APPROVAL

The study was approved by the Ethics Commission of Shanghai Jiao Tong University (ref. no. B2021120I). The written informed consent was obtained from each participant.

Supporting information

Supporting Information

Lai, D. Y. , Xue, J. B. , He, P. , Jiang, H. , Li, Y. , Ma, M. L. , Hong, W. , Yu, J. P. , Wei, H. P. , & Tao, S. C. (2023). Longitudinal neutralization activities on authentic Omicron variant provided by three doses of BBIBP‐CorV vaccination during one year. Proteomics, 23, e2200306. 10.1002/pmic.202200306

DATA AVAILABILITY STATEMENT

The SARS‐CoV‐2 protein microarray data are deposited on Protein Microarray Database under the accession number PMDE261 (http://www.proteinmicroarray.cn). Additional data related to this paper may be requested from the corresponding author.