Analysis of the level of protective serum antibody after third dose of different COVID-19 vaccines

A new coronavirus (SARS-CoV-2), causing COVID-19 (coronavirus disease 2019), is a member of the Coronaviridae family. The benefits of the primary COVID-19 vaccination far outweigh the risks. Nevertheless, the risks associated with too early and too frequent boosters should be considered, especially when vaccines have immune-mediated effects like myocarditis, which is more commonly associated with the second dose of some mRNA vaccines. Booster vaccinations against SARS-CoV-2 are needed because of either reduced immunity to the original vaccine or evolved viruses producing immunity to the initial vaccine antigens. So, the aim of this study was to detect the difference in neutralizing anti-RBD antibodies between the third and second doses of COVID-19 vaccines. A study was performed among 29 eligible participants in Birjand (Iran). Blood samples were taken from all participants 2–4 weeks after the third dose. In the next step, humoral responses were assessed with a kit detecting neutralization of SARS-CoV-2. SPSS software version 22.0 (SPSS Inc., Chicago, IL) was used to analyze the data. The mean age of cases was 35.62 ± 8.72 years, with a range of 21–53 years. The obtained results showed that all vaccines significantly had a higher efficacy in the third dose than the second. Participants who received Vaxzevria in the second dose and PastoCovac Plus in the third dose had more immunogenicity. According to the results of this study, a third dose of the vaccine should be given to persons aged ≥ 20 years to provide an increased level of protection against COVID-19. Especially, participants who received Sputnik-V and Vaxzevria in the second dose and PastoCovac Plus in the third dose showed a more effective immune response against the virus.