Vaccines, Vol. 12, Pages 180: Long-Term Dynamic Changes in Hybrid Immunity over Six Months after Inactivated and Adenoviral Vector Vaccination in Individuals with Previous SARS-CoV-2 Infection

Vaccines, Vol. 12, Pages 180: Long-Term Dynamic Changes in Hybrid Immunity over Six Months after Inactivated and Adenoviral Vector Vaccination in Individuals with Previous SARS-CoV-2 Infection

Vaccines doi: 10.3390/vaccines12020180

Authors: Nungruthai Suntronwong Sitthichai Kanokudom Chompoonut Auphimai Thanunrat Thongmee Suvichada Assawakosri Preeyaporn Vichaiwattana Ritthideach Yorsaeng Thaneeya Duangchinda Warangkana Chantima Pattarakul Pakchotanon Pornjarim Nilyanimit Donchida Srimuan Thaksaporn Thatsanathorn Natthinee Sudhinaraset Nasamon Wanlapakorn Yong Poovorawan

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-γ 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-naïve, 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-γ level at six months returned to pre-vaccination levels. However, more individuals exhibited reactive T cell responses. Extending the interval (13–15 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.