Assessment of Reactivity to the Administration of the mRNA Vaccine after Six Months of Observation

Background: The fast spread of the SARS-CoV-2 virus accelerated efforts to create an effective vaccine, and a novel mRNA vaccine was the first to appear effective. Scientific evidence regarding mRNA vaccination is limited; therefore, understanding how the immune system responds to an mRNA vaccine is critical. Our study was aimed at a long-term analysis of the presence and maintenance of the immune response using the chemiluminescent method by analyzing the level of IgG antibodies in vaccinated people who were and were not infected with the SARS-CoV-2 virus. Materials and methods: Healthcare workers with a history of COVID-19 or who were naïve to the infection were recruited for this study and administered two subsequent doses of the Comirnaty vaccine. IgG SRBD antibody levels were evaluated every month for six consecutive months using the chemiluminescent immunoassay (CLIA). Results: A total of 149 individuals were recruited for this study, 68 had evidence of past COVID-19 infection, with 63 exhibiting elevated IgG SRBD antibody levels at initial evaluation. Statistically significant differences were observed between COVID-19 convalescents and non-convalescents at all study time points, with the convalescent group consequently representing higher antibody levels. Conclusions: COVID-19 convalescents showed a stronger immune response to the vaccine after the first dose. This group exhibited higher IgG levels in all examinations during the observation period. The natural waning of antibody levels can be observed within six months. A booster vaccination may be required. No serious side effects were observed.