The comparison of Immune response to Third booster dose with of Vaxzevria or Comirnaty COVID-19 vaccine in healthcare workers after receiving two doses of CoronaVac

The COVID-19 outbreak has significantly impacted public health, with vaccine effectiveness being crucial for control. The efficacy of heterologous prime-boost vaccines remains unclear. This study compared Vaxzevria and Comirnaty as booster doses given 90 days after two CoronaVac doses. Participants who received two CoronaVac doses at least 90 days earlier chose either the Vaxzevria or Comirnaty booster based on individual preference. Anti-Spike receptor-binding domain (anti-S-RBD) IgG levels were measured on days 14, 28, and 90, and surrogate virus neutralization tests (sVNT) were conducted on days 14 and 90. A total of 100 participants were enrolled (36 males and 64 females). Participants in the Vaxzevria group were older, while the priming-to-booster interval was longer in the Comirnaty group (both p < 0.05). Anti-S-RBD IgG levels and neutralizing activity against the Delta variant increased significantly after booster vaccination in both groups. Unadjusted analyses showed higher antibody levels in the Comirnaty group at all time points. However, after adjustment for baseline differences using multivariable regression and propensity score matching, post-booster antibody responses were more strongly associated with host factors, particularly age and body mass index, than with booster platform. In individuals previously vaccinated with two doses of CoronaVac, both Comirnaty and Vaxzevria boosters substantially enhanced humoral and neutralizing immune responses against the Delta variant. After adjustment for baseline differences, host characteristics played a more prominent role than booster platform in determining short-term immunogenicity.