Effect of age and prior COVID-19 on BBIBP-CorV (Sinopharm) vaccination- induced antibody responses in a region with high seroprevalence

Abstract Introduction Sinopharm (BBIBP-CorV) inactivated virus vaccination for COVID-19 has been administered widely in Pakistan. We investigated the dynamics of BBIBP-CorV -induced antibody responses over a 24 week period in a region with a high seroprevalence. Methods Study subjects (n = 312) were followed up over a 24-week period between May and August 2021. Sera were tested for IgG antibodies to spike and the receptor binding domain (RBD). Results Study subjects were 62% female. Twenty-two percent had a prior history of COVID-19. At 4-, 8- 16- and 24-weeks post-vaccination, the rate of IgG antibodies positive to spike was 57%, 87%, 66% and 90% of individuals, compared with to RBD which was 48%, 62%, 68% and 85% of subjects, respectively,. IgG to spike and RBD showed a positive correlation at each interval (rho > 0.6, p < 0.0001). Seropositivity to both spike and RBD was reduced in those aged 50 years and over for up until 16 weeks post-vaccination (p < 0.05). Individuals with prior COVID-19 infection showed greater antibody responses for up to 16 weeks post-vaccination (p < 0.05). SARS-CoV-2 infections were observed with a mean interval of 16 weeks post-vaccination. Antibody responses did not wane for up to 6 months post-vaccination. Conclusions Sinopharm vaccination-induced antibody responses were negatively impacted by age and positively impacted by prior COVID-19 for 16 weeks after vaccination. Importantly, we did not find waning of IgG antibodies to RBD over the study period. Maintenance of antibodies may be the result of continued community exposure and boosting with COVID-19 vaccination.