Acquired neutralizing breadth against SARS-CoV-2 variants including Omicron after three doses of mRNA COVID-19 vaccination and the vaccine efficacy

ABSTRACT

To investigate the induction of neutralizing antibodies against Omicron after two and three vaccine doses in recipients of different ages. Physicians at Kobe University Hospital who had received the second dose of the BNT162b2 mRNA vaccine. At 2 months after the second vaccinations, the positive rate of neutralizing antibody against Omicron was 28%, and the titer was significantly lower than those against other variants, 11.8-fold and 3.6-fold lower than those against D614G and Delta, respectively. Unlike Delta, that positive rates of neutralizing antibody against Omicron were low in all age groups, and there was no significant difference in titers among age groups. Seven months after the 2nd dose, the positive rate of neutralizing antibody against Omicron decreased to 6%, but after the booster,3rd vaccination, it increased to 100%, and the titer was much higher than those at 2 and 7 months post-vaccination, 32-fold and 39-fold respectively. The booster vaccination effect was also observed in the younger at 41-fold, middle-aged at 43-fold, and older at 27-fold groups compared to the 7-month titers. Surprisingly, higher-than-predicted titers of the neutralizing antibodies against Omicron were induced after the booster vaccination regardless of recipient age, while this effect was not observed after two doses, indicating the induction of antibodies against common epitopes by the booster vaccination. Three doses can be confidently recommended to suppress the pandemic.