Humoral immune response in inactivated SARS-CoV-2 vaccine: When should a booster dose be administered?
Abstract
Background
For a sustained and essential protective antibody response, it is important to understand how long the humoral immune response induced by the SARS-CoV-2 inactivated vaccine persists.
Aims
This study aimed to detect the first and third-month concentrations and seroconversion rates of the antibodies induced by the inactivated vaccine.
Study Design
This is a vaccine efficacy study.
Methods
The study included 272 health workers who were vaccinated at days 0 and 28 by the inactivated SARS-CoV-2 vaccine (3μg/0.5ml). Anti-S-RBD-IgG and total anti-spike/anti- nucleocapsid-IgG antibody concentrations and seroconversion rates were examined in vaccinated health workers at the 1 st and 3 rd months after the vaccination. The test method used for the qualitative detection and differentiation of IgG antibodies (indirect method) to SARS-CoV-2 is a chemiluminescence reaction (CLIA).
Results
The mean age of the health workers was 38.93±10.59 (min:21-max:64). A total of 45(16.5%) participants declared to have had COVID-19 before the first dose of the inactivated vaccine. The participants were found to be reactive for anti-S-RBD-IgG antibodies by 98.2% and 97.8% at the first and third months, respectively, after the administration of the second dose. The decrease in the mean plasma concentrations of anti-S-RBD IgG was observed as 56.7% in the cohort with only two doses of the vaccine (1 st month:42.4AU/ml versus 3 rd month: 18.2AU/ml). In the cohort with a history of COVID-19 prior to the vaccination, the decrease was observed as 25.1% (1 st month:58.29 versus 3 rd month:43.64 AU/ml) and at a mean of 57.4 (0-90) days prior to vaccination, the decrease was of 43.1% (1 st month:55.05 AU/ml versus 3 rd month:31.28 AU/ml), keeping more stable in participants infected at a mean of 183.1 (91-330) days prior to vaccination (a decrease of 5.2%; with 62.34 AU/ml at 1 st and 59.08 AU/ml at 3 rd months). Anti-S-RBD concentrations were observed to increase 10-fold (30.44 AU/ml at 1 st and 310.64 AU/ml at 3 rd months) in participants infected after the vaccination and to decrease among people aged 50 years and older.
Conclusion
Antibody concentrations at the 1 st and 3 rd months after the vaccination with two doses of the inactivated SARS-CoV-2 vaccine were found to be decreased, but still detectable (except in one participant). As participants who had COVID-19 at a mean of 181 (90-330) days before the vaccination presented with a more stable antibody level, it can be concluded that a booster at months 6-12, resulting in a schedule of 0-1-6 months, is recommended for the inactive SARS-CoV-2 vaccination.
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