Mixing versus matching booster vaccines: A longitudinal humoral immune kinetics against Omicron in a Malaysian cohort.

OBJECTIVE: The objective of our study was to evaluate the longitudinal humoral immune response following booster regimens in Malaysia during the Omicron outbreak. METHODS: In this prospective cohort study, 268 healthcare professionals and medical students in Malaysia were followed up for 24 weeks following homologous (mRNA-mRNA (mR-mR), viral vector-viral vector (VV-VV), inactivated virus-inactivated virus (IV-IV) and heterologous (inactivated virus-mRNA (IV-mR), viral vector-mRNA (VV-mR) booster vaccines. Of them, 190 recipients underwent longitudinal immunogenicity study. Anti-S IgG and anti-RBD response were assessed by ADVIA Centaur SARS-CoV-2 chemiluminescent immunoassay followed by surrogate virus neutralization test using Omicron-variant across all boosters. RESULTS: Compared to homologous boosters, heterologous regimens, particularly the IV-mR booster, elicited significantly higher and sustained anti-S IgG and anti-RBD antibody (P<0.0001) responses. Over 24 weeks, the heterologous IV-mR booster had 100% seropositive anti-S IgG and anti-RBD antibodies, conversely, in the homologous (IV-IV) booster, the seropositivity of anti-S IgG and anti-RBD antibody reduced to 15.63% and 18.75% respectively. Omicron-virus neutralizing activity was observed as high as 95.92% (IV-mR) and 83.87% (VV-mR) following W24 of the heterologous booster, while virus neutralization was found as low as 9.38% in the IV-IV homologous booster. Age, gender, and ethnicity were not found as confounding factors for antibody kinetics following booster vaccine. CONCLUSION: In conclusion, heterologous booster vaccines induced superior prolonged humoral-immune response against COVID-19 infection.