The immunogenicity and reactogenicity of four COVID-19 booster vaccinations against SARS-CoV-2 variants of concerns (Delta, Beta, and Omicron) following CoronaVac or ChAdOx1 nCoV-19 primary series

The CoronaVac (Sinovac Biotech) and ChAdOx1(Oxford-AstraZeneca) are two widely used COVID-19 vaccines. We examined the immunogenicity of four COVID-19 booster vaccine: BBIBP-CorV (Sinopharm Biotech), ChAdOx1, 30μg-BNT162b2 and 15μg-BNT162b2 (Pfizer-BioNTech), in healthy adults who received a two-dose CoronaVac or ChAdOx1 8-12 weeks earlier. Among the 352 participants (179 CoronaVac and 173 ChAdOx1 participants), 285 (81%) were female, and median age was 39(IQR: 31-47) years. 98%(175/179) and 99%(172/173) of Coronavac and ChAdOx1 participants remained seropositive at baseline. Two weeks post-booster, both 30μg- and 15μg-BNT162b2 induced the highest anti-RBD IgG concentration (BAU/mL); Coronavac-prime: 30μg-BNT162b2, 5152.2(95%CI 4491.7-5909.8); 15μg-BNT162b2, 3981.1(3397.2-4665.4); ChAdOx1, 1358.0(1141.8-1615.1); BBIBP-CorV, 154.6(92.11-259.47); ChAdOx1-prime: 30μg-BNT162b2, 2363.8(2005.6-2786.1; 15μg-BNT162b2, 1961.9(1624.6-2369.1); ChAdOx1, 246.4(199.6-304.2); BBIBP-CorV, 128.1(93.5-175.4). Similarly, both 30μg- and 15μg-BNT162b2 boosting induced the highest neutralizing antibodies (nAb) titres against all variants and highest T-cell response evaluated by interferon gamma released asssays. While all BNT162b2 or heterologous ChAdOx1-boosted participants had nAb against Omicron, these were <50% for BBIBP-CorV and 75% for homologous ChAdOx1-boosted participants. There was significant decrease in nAb (>4-fold) 16-20 weeks post booster. Heterologous boosting with BNT162b2 following CoronaVac or ChAdOx1 primary series is most immunogenic. A lower dose BNT162b2 may be considered as booster in settings with limited vaccine supply.