Long-Term Dynamic Changes in Hybrid Immunity over Six Months after Inactivated and Adenoviral Vector Vaccination in Individuals with Previous SARS-CoV-2 Infection

Abstract

Numerous studies have largely focused on short-term immunogenicity in recovered individuals post mRNA vaccination. However understanding the long-term durability particularly in inactivated and adenoviral vectored vaccines remains limited. We evaluated antibody responses omicron variant neutralization and IFN-? responses in 119 previously infected individuals vaccinated with CoronaVac or ChAdOx1 up to six months post-vaccination. Both vaccines elicited robust immune responses in recovered individuals surpassing those who were infection-na?ve and these persisted above pre-vaccination levels for six months. However antibody levels declined over time (geometric mean ratio (GMR) = 0.52 for both vaccines). Notably neutralizing activities against omicron declined faster in ChAdOx1 (GMR = 0.6) compared to CoronaVac recipients (GMR = 1.03). While the first dose of ChAdOx1 adequately induced immune responses in recovered individuals a second dose demonstrated advantages in omicron variant neutralization and slower decline. Although both vaccines induced T cell responses the median IFN-? level at six months returned to pre-vaccination levels. However more individuals exhibited reactive T cell responses. Extending the interval (13� months) between infection and vaccination could enhance antibody levels and broaden neutralization. Together these findings demonstrate a robust humoral and cellular response that was sustained for at least six months after vaccination thus guiding optimal vaccination strategies based on prior infection and vaccine platforms. ? 2024 by the authors.