Keywords
COVID-19, neutralizing antibody, CoronaVac, anti-SRBD, Sinovac
This article is included in the Emerging Diseases and Outbreaks gateway.
This article is included in the Coronavirus collection.
COVID-19, neutralizing antibody, CoronaVac, anti-SRBD, Sinovac
Prevention of severe coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its associated mortality is still a major hurdle worldwide. The disease is associated with several long-term consequences.1,2 To date, no truly effective antivirals or therapeutic strategy has been successfully developed for the treatment of critical COVID-19. Some drugs, such as remdesivir and hydroxychloroquine, showed limited efficacy.3,4 The presence of individual protective immunity, instead, could provide effective protection against acute SARS-CoV-2 infection.5 Therefore, understanding and profiling antibody response towards SARS-CoV-2 is highly prominent as it will provide significant insight into therapeutic approaches. Specific antibodies detection, as an indirect method for COVID-19 diagnosis, allows the evaluation of seroprevalence, promoting a better understanding of the COVID-19 transmission among communities. It also enables the identification of individuals potentially invulnerable to SARS-CoV-2 infection, monitoring of herd immunity, as well as formulating strategies for global COVID-19 vaccination.6–8
Neutralizing antibodies (NAbs) provide real protective immunity as they play a crucial role in hampering the binding of the SARS-CoV-2 receptor-binding domain (RBD) of surface spike (S) protein to the human angiotensin-converting enzyme 2 (ACE2) receptor,9–12 blocking viral infection and minimizing disease severity. Therefore, measuring SARS-CoV-2 NAbs is considered an acceptable approach for the analysis of protective immune response against COVID-19 after vaccination.13
Vaccination triggers the neutralizing immune response, making vaccination an effective strategy to control virus-associated diseases although the acceptance rate varies among countries.14,15 Vaccination programs for COVID-19 using various vaccine types have therefore been vigorously conducted, including the inactivated CoronaVac.16 Preclinical studies revealed the ability of CoronaVac to induce NAb production as well as providing partial and complete protection in the tested animals against COVID-19.17 This vaccine has also been reportedly well tolerated and induced the humoral immune responses in individuals aged 18–59 years.18 However, given the fact that reinfection still occurred in individuals vaccinated with CoronaVac and the vaccine-induced NAb titres have been reportedly waning over time, it is questionable to what extent this vaccine can persist and protect against SARS-CoV-2. Therefore, evaluating NAb response in individuals within a different duration of time upon CoronaVac vaccination is critically important, as it may serve as a predictor of vaccine protection efficacy. This study sought to evaluate the titre of anti-SARS-CoV-2 NAbs among CoronaVac-vaccinated individuals as well as to determine the potential factors associated with the level of the titre.
A cross-sectional study among COVID-19-vaccinated residents in Banda Aceh, Indonesia was conducted from May to July 2021. The subjects were post COVID-19-vaccinated individuals residing in Banda Aceh who met the inclusion criteria. Individuals vaccinated with two doses of CoronaVac vaccine (Sinovac Biotech) within one to six months prior to the recruitment period, had never been diagnosed with COVID-19, and aged between 18 and 65 years were considered eligible for the study. Individuals who had COVID-19 after the vaccination or having symptoms during the period of recruitment and having malignant diseases were excluded. The recruitment was conducted based on COVID-19 vaccination records obtained from Prince Nayef Hospital Universitas, Syiah Kuala, Banda Aceh, Indonesia.
The response variable was the level of SARS-CoV-2 NAb titre after CoronaVac vaccination, measured using ELISA. Several plausible factors that might be associated with the NAb titre were measured and collected. This included demographic characteristics such as age and gender, body mass index (BMI), history of illness, history of immunization (BCG and influenza), adverse events following vaccination (allergy, fever, arthralgia, and acute paralysis), exercise routine, smoking status, comorbidities (hypertension, diabetes, hyperlipidaemia, chronic obstructive pulmonary disease (COPD), asthma, and gout), sleep quality, and level of stress. BMI was measured by measuring participant height and weight. A set of standardized and validated questionnaires were used: (a) the quality of sleep was assessed according to Pittsburgh Sleep Quality Index (PSQI)19; and (b) the level of stress was determined based on the Depression Anxiety Stress Scales 42 (DASS-42).20
The venous blood was collected and centrifuged to separate the sera. The sera were stored at -80°C until used. Specific anti S-RBD NAb titre was measured through an electrochemiluminescence immunoassay (ECLIA) method using Elecsys® Anti-SARS-CoV-2 S immunoassay following the manufacturer’s instruction (Roche Diagnostics International Ltd, Rotkreuz, Switzerland). The assay was conducted using an automatic Roche cobas® E411 immunoassay analyzer (Roche Diagnostics International Ltd, Rotkreuz, Switzerland). The assay uses a recombinant protein representing the RBD of the S antigen in a double-antigen sandwich assay approach. In brief, 20 μL of sample incubated with SARS-CoV-2-Ag~biotin (a biotinylated SARS-CoV-2 S-RBD-specific recombinant antigen) and SARS-CoV-2 Ag~Ru (bpy) (SARS-CoV-2 S-RBD-specific recombinant antigen labeled with a ruthenium complex) instruction (Roche Diagnostics International Ltd, Rotkreuz, Switzerland). The complex became bound to the solid phase after streptavidin-coated microparticles were added. The reaction mixture was aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. The chemiluminescent emission was then measured by a photomultiplier. The titres of the SARS-CoV-2 NAb were then classified as protective and non-protective using a cut-off 15 U/mL.21
Analysis of variance (Anova) and Student t-test were used to compare the titres of SARS-CoV-2 NAb between demographic groups as appropriate. Linear regression was employed to determine factors affecting the NAb titre. Pearson correlation was used to assess the correlation between day of post vaccination, age and BMI with the titres of NAb. The analyses were conducted using SPSS version 20 (IBM SPSS Inc., Chicago, IL, USA) (RRID:SCR_019096).
This study was approved by the Health Research Ethics Committee of the Faculty of Medicine, Universitas Syiah Kuala - Zainoel Abidin Hospital (#198/EA/FK-RSUDZA/2021 and KEPPKN Registration #1171012P). All the participants were informed of the study procedures and provided written consent prior to participating in this study.
We measured the level of SARS-CoV-2 NAb titre in individuals with different length of time post the second dose. The individual titres and the mean titres of SARS-CoV-2 NAb from each group are presented in Figure 1. The mean of titre of the one-month group was 184.5 IU/mL and the mean decreased to 101.8 IU/mL in samples collected from those five-month post-vaccination and to 95.5 IU/mL in the six-month group. All samples from one to three months post-vaccination had protective SARS-CoV-2 NAb titres (more than 15 IU/mL). However, only 78.9% of the samples from six-months post-vaccination had a protective level of NAb titres against SARS-CoV-2.
We assessed the association of some plausible factors with the titre of SARS-CoV-2 NAb (Table 1). Our data suggested that healthy meal intake was associated with the NAb titres. The titre of NAb anti-SRBD was higher in those who took regular healthy meal compared to those who did not (136.7 vs. 110.4 IU/mL, p = 0.044) (Table 1). When we included only those who were vaccinated within five to six months (n = 76), only regular healthy meal intake was associated with the level of SARS-CoV-2 NAb anti-SRBD (79.0 vs 134.5 IU/mL) (Table 2).
Our data suggest that the length of post-vaccination time was associated with the NAb titres after adjustment (Table 1). Compared to those in first month of vaccination, the level of NAb titres were significantly lower from individuals five months-post vaccination (184.6 vs. 101.8 IU/mL, p = 0.009). Similarly, the level of NAb titres was significantly lower in samples from individuals six-months post vaccination (184.6 vs. 95.59 IU/mL, p = 0.001) (Table 1). Spearman’s rank correlation (rs) also showed that the time of post vaccination was correlated negatively with antibody anti-SRBD titre (Table 3). This indicated that the longer time post-vaccination the lower NAb anti-SRBD titre.
Our results revealed waning neutralizing immunity in individuals after vaccination with CoronaVac vaccine. We noted a significant decline in the level of SARS-CoV-2 NAb titre five and six months after the receipt of the second dose of the vaccine when compared to the first month (Figure 1 and Table 1), suggesting that the time of post vaccination was negatively correlated with antibody anti-SRBD titre. Reduction in vaccine-induced neutralization titres within the first six months upon the second dose vaccination has also been previously reported in several different vaccines.22–25 However, a similar study suggested that the decrease in CoronaVac-induced anti-S antibodies levels was faster in individuals without prior SARS-CoV-2 infection compared to those with previous infection.26 NAbs can persist in the body for two to 12 months after the infection onset.5,27 This might suggest that CoronaVac would assumingly provide greater and longer-lasting protective impact when administered in previously infected individuals, as it may boost the memory immune cells that developed following the infection.27,28
The underlying causes of rapid waning of vaccine induced NAbs remains to be determined. However, several studies reported that waning NAb titres have been associated with IgG anti-RBD immune response29,30 and neutralizing capacity was positively correlated with IgG antibody titres.31 Furthermore, the loss of short-lived plasma cells has been considered the cause of initial rapid waning of antibodies in SARS-CoV-2 infected individuals in general, while establishment of long-lived plasma was thought to contribute to the elevation of antibody level.32,33 Defective Bcl6+ follicular T-cells due to the absence of germinal centers in the thoracic lymph nodes in dead COVID-19 patients was proposedly unable to activate memory B-cells, leading to a decrease in long-lasting and high-affinity antibody production.34 This mechanism has been suggested as a potential explanation regarding rapid antibody decline in SARS-CoV-2.34
This study suggested that more than 20% of the sample of five- and six-month post-vaccination had NAb titres <15 IU/mL compared to those of one to three months, suggesting a loss of protection after three months of vaccination against SARS-CoV-2 (Table 2). Reduction in the level of protective antibody might be due to the decreased NAb titres as waning antibody titres have been reportedly correlated with reduced protection over time.12,25,35 This remarkable reduction in the titre of SARS-CoV-2 NAb anti-SRBD and its decline in protective level might indicate the need for an additional booster dose of CoronaVac vaccine to protect against COVID-19 among individuals without prior SARS-CoV-2 infection.
Our findings suggested the level of SARS-CoV-2 NAb anti-SRBD was significantly associated with a regular intake of healthy meals, regardless of the duration post-vaccination (Tables 1 and 2). An adequate intake of vitamins such as vitamin A, B12, B6, and C, zinc, as well as iron is suggested to maintain immune function, particularly during COVID-19.36 Vitamin C has been known to boost the immune system and prevent any viral infection.36,37 Healthy meals and optimal nutritional intake will impact the immune system through cell activation, signalling molecule modification, and gene expression. A variety of dietary components also determines the composition of gut microbes which then form the immune response in the body.38
We assessed the level of anti-SARS-CoV-2 neutralizing antibody titre in CoronaVac-vaccinated individuals. Our data indicated that the level of NAb titres dropped significantly within five and six months after the second dose of CoronaVac vaccination, along with the decay of protective capacity in several samples. Our study suggested that the length of time post-vaccination negatively correlated with the level of NAb titres. Regular healthy meal intake was associated significantly with the level of NAb, regardless of the duration post-vaccination. This provided a prediction of CoronaVac vaccine efficacy in protecting individuals against SARS-CoV-2 infection over time upon the second dose vaccination. This may contribute to future vaccination policy management to improve and prolong the protective strategy through vaccination.
Figshare: Underlying data for ‘Waning anti-SARS-CoV-2 neutralizing antibody in CoronaVac-vaccinated individuals in Indonesia’. https://doi.org/10.6084/m9.figshare.19149797.39
This project contains the following underlying data:
Figshare: STROBE checklist for ‘Waning anti-SARS-CoV-2 neutralizing antibody in CoronaVac-vaccinated individuals in Indonesia'. https://doi.org/10.6084/m9.figshare.19149806.40
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).
The authors would like to thank to staff at Dr. Imai Indra Laboratory, Prince Nayef Hospital Universitas Syiah Kuala, and Prodia Laboratory Banda Aceh, Indonesia, for assistance during the study. We would like to thank Narra Studio Jurnal Indonesia for its assistance during the manuscript preparation.
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Is the work clearly and accurately presented and does it cite the current literature?
Partly
Is the study design appropriate and is the work technically sound?
Partly
Are sufficient details of methods and analysis provided to allow replication by others?
Yes
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
References
1. Sánchez-Sendra B, Albert E, Zulaica J, Torres I, et al.: Neutralizing antibodies against SARS-CoV-2 variants of concern elicited by the comirnaty COVID-19 vaccine in nursing home residents. Scientific Reports. 2022; 12 (1). Publisher Full TextCompeting Interests: No competing interests were disclosed.
Reviewer Expertise: SARS-CoV-2 immunology, SARS-CoV-2 vaccine trial.
Is the work clearly and accurately presented and does it cite the current literature?
Yes
Is the study design appropriate and is the work technically sound?
Yes
Are sufficient details of methods and analysis provided to allow replication by others?
Yes
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Public health, infection control and prevention, psychiatric epidemiology.
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Version 1 10 Mar 22 |
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