Avaliação da resposta imune humoral ao SARS-CoV-2 induzida pela vacinação contra a COVID-19 no Acre, Brasil

Abstract

The SARS-CoV-2 pandemic emerged as a global health challenge. The highly transmissible and mutable virus posed a severe threat to public health, and widespread vaccination of the world's population was crucial to control transmission, prevent severe cases, and reduce covid-19 deaths. In this context, understanding the humoral immune response to different vaccination strategies is fundamental to contributing to future immunization policies. Objective: To determine the variation in the humoral immune response of IgG antibodies against SARS-CoV-2 according to the vaccination regimen received by participants in Rio Branco, Acre, Brazil. Methods: This research was conducted in Rio Branco – Acre. Considering the Pfizer-BioNTech BNT162b2 vaccines (monovalent and bivalent) as booster doses, pre- and post-vaccination blood samples were collected from participants who received the 3rd, 4th, or 5th dose (classified into groups according to the booster number). Data collection from study individuals included demographic information, vaccination history, previous SARS-CoV-2 infection, physical activity level, and complete blood count data, while antibody analysis was performed using the ELISA technique, with the reactivity index (IR) to evaluate anti-Spike and anti-RBD IgG levels. Statistical analysis aimed to compare the influence of the administered vaccine on the humoral immune response, with the objective of determining the relationship between vaccination and immunity in the region. A p-value < 0.05 was adopted as the level of significance. Results: The study included 150 individuals. Of these, 39 (26%) received the 3rd monovalent dose, and 7 (4.7%) also received a 4th bivalent dose. The remaining 111 individuals (74%) received the 4th monovalent dose, and among these, 23 (15.3%) also received a 5th bivalent dose. It was observed that the 3rd monovalent dose significantly increased anti-Spike (22.99→27.32 IR; p<0.0001) and anti-RBD (16.97→17.36 IR; p=0.001) IgG levels, while the 4th monovalent dose had a smaller effect compared to the 3rd monovalent dose (anti-Spike: 24.35→26.57 IR, p<0.0001; anti-RBD: 17.71→17.89 IR, p=0.0111), suggesting a possible plateau effect in the response. The bivalent vaccine (5th dose) specifically increased anti-RBD (18.30→18.68 IR; p=0.0039). Women showed more robust immune responses, and both vaccination regimens (homologous and heterologous) were effective, without significant influence of previous infection history or physical activity on antibody levels. The use of medication for symptoms was 8 times more likely in individuals with adverse reactions than in those without (OR = 7.9895; p < 0.05). The observed changes in complete blood counts after vaccination remained within reference ranges. Conclusion: Booster doses in SARS-CoV-2 vaccination are notable for their ability to increase and/or sustain the production of IgG antibodies specific to different SARS-CoV-2 antigens. Maintaining a robust immunological response through additional doses is fundamental as part of ongoing vaccination strategies aimed at effectively protecting the population against covid19. Relevance: Evaluation of the humoral immune response to different covid-19 vaccination regimens, with emphasis on the role of booster doses in increasing antibody production. The results can optimize vaccine booster strategies and identify factors influencing the magnitude and duration of immunity. Impact: To inform public health decisions by improving the effectiveness of vaccination campaigns and reinforcing public confidence in immunization, thereby contributing to collective protection and control of SARS-CoV-2 infection.