Comparison of the immunogenicity of BNT162b2 and CoronaVac COVID-19 vaccines in Hong Kong

Background and objective: Few head-to-head evaluations of immune responses to different vaccines have been reported. Methods: Surrogate virus neutralization test (sVNT) antibody levels of adults receiving either two doses of BNT162b2 (n = 366) or CoronaVac (n = 360) vaccines in Hong Kong were determined. An age-matched subgroup (BNT162b2 [n = 49] vs. CoronaVac [n = 49]) was tested for plaque reduction neutralization (PRNT) and spike-binding antibody and T-cell reactivity in peripheral blood mononuclear cells. Results: One month after the second dose of vaccine, BNT162b2 elicited significantly higher PRNT₅₀, PRNT₉₀, sVNT, spike receptor binding, spike N-terminal domain binding, spike S2 domain binding, spike FcR binding and antibody avidity levels than CoronaVac. The geometric mean PRNT₅₀ titres in those vaccinated with BNT162b2 and CoronaVac vaccines were 251.6 and 69.45, while PRNT₉₀ titres were 98.91 and 16.57, respectively. All of those vaccinated with BNT162b2 and 45 (91.8%) of 49 vaccinated with CoronaVac achieved the 50% protection threshold for PRNT_90. Allowing for an expected seven-fold waning of antibody titres over 6 months for those receiving CoronaVac, only 16.3% would meet the 50% protection threshold versus 79.6% of BNT162b2 vaccinees. Age was negatively correlated with PRNT₉₀ antibody titres. Both vaccines induced SARS-CoV-2-specific CD4⁺ and CD8⁺ T-cell responses at 1 month post-vaccination but CoronaVac elicited significantly higher structural protein-specific CD4⁺ and CD8⁺ T-cell responses. Conclusion: Vaccination with BNT162b2 induces stronger humoral responses than CoronaVac. CoronaVac induces higher CD4⁺ and CD8⁺ T-cell responses to the structural protein than BNT162b2.