Comparable and sustained levels of S1-RBD-IgG and S1-RBD-IgA in BNT162b2 homologous and CoronaVac-BNT162b2 heterologous booster vaccination: A 22-month prospective study in Malaysia

This prospective cohort study examines the long-term humoral immune responses post-COVID-19 vaccination in 146 individuals who received either a homologous three-dose BNT162b2 vaccine regimen (PPP) or two primary doses of CoronaVac followed by BNT162b2 booster (SSP) in Malaysia. The study focuses on serum anti-S1-RBD-IgG, -IgA, and -IgM, using the ELISA method. The results show that BNT162b2 outperformed CoronaVac in the two dose primary vaccination series. BNT162b2 booster dose significantly raised serum anti-S1-RBD-IgG and -IgA levels, sustaining this increase from 26 to 52 weeks after administration, regardless of the vaccine regimen. This leads to equivalent levels of anti-S1-RBD-IgG and -IgA after boosting with BNT162b2 in both groups. Breakthrough infections, particularly with the emergence of the Omicron variant, did not result in increased anti-S1-RBD-IgG and -IgA levels. No significant induction of anti-S1-RBD-IgM was observed following multiple vaccine doses. The long-term investigation revealed that PPP and SSP groups had comparable humoral immune responses to SARS-CoV-2, highlighting the advantage of mRNA booster dose in our cohort.