Abstract
Background: Waning protection against emerging SARS-CoV-2 variants by pre-existing antibodies elicited due to current vaccination or natural infection is a global concern. Whether this is due to the waning of immunity to SARS-COV-2 remains unclear.Aim: We aimed to investigate the dynamics of antibody isotype responses among vaccinated naïve (VN) and naturally infected (NI) individuals.Methods: We followed up antibody levels in COVID-19 mRNA-vaccinated subjects without prior infection (VN, n = 100) in two phases: phase-I (P-I) at ~ 1.4 and phase-II (P-II) at ~ 5.3 months. Antibody levels were compared to those of unvaccinated and naturally infected subjects (NI, n = 40) at ~ 1.7 (P-1) and 5.2 (P-II) months post-infection. Neutralizing antibodies (NTAb), anti-S-RBD-IgG, -IgM, and anti-S-IgA isotypes were measured.Results: The VN group elicited significantly greater antibody responses (p < 0.001) than the NI group at P-I, except for IgM. In the VN group, a significant waning in antibody response was observed in all isotypes. There was about ~ a 4-fold decline in NTAb levels (p < 0.001), anti-S-RBD-IgG (~5-folds, p < 0.001), anti-S-RBD-IgM (~6-folds, p < 0.001), and anti-S1-IgA (2-folds, p < 0.001). In the NI group, a significant but less steady decline was notable in S-RBD-IgM (~2-folds, p < 0.001), and a much smaller but significant difference in NTAb (<2-folds, p < 0.001) anti-S-RBD IgG (<2-folds, p = 0.005). Unlike the VN group, the NI group mounted a lasting anti-S1-IgA response with no significant decline. Anti-S1-IgA, which were ~ 3 folds higher in VN subjects compared to NI in P-1 (p < 0.001), dropped to almost the same levels, with no significant difference observed between the two groups in P-II.Conclusion: While double-dose mRNA vaccination boosted antibody levels, vaccinated individuals' 'boost' was relatively short-lived. [ABSTRACT FROM AUTHOR]