Ancestral SARS‐CoV‐2 and Omicron BA.5‐specific neutralizing antibody and T‐cell responses after Omicron bivalent booster vaccination in previously infected and infection‐naive individuals

Abstract

AbstractCoronavirus disease‐2019 (COVID‐19) bivalent ancestral/Omicron messenger RNA (mRNA) booster vaccinations became available to boost and expand the immunity against severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) Omicron infections. In a prospective cohort study including 59 healthcare workers, we assessed SARS‐CoV‐2 ancestral and Omicron BA.5‐specific neutralizing antibody and T‐cell responses in previously infected and infection‐naive individuals. Also, we assessed the effect of an ancestral/Omicron BA.1 bivalent mRNA booster vaccination on these immune responses. 10 months after previous monovalent mRNA vaccinations, ancestral SARS‐CoV‐2 S1‐specific T‐cell and anti‐RBD IgG responses remained detectable in most individuals and a previous SARS‐CoV‐2 infection was associated with increased T‐cell responses. T‐cell responses, anti‐RBD IgG, and Omicron BA.5 neutralization activity increased after receiving an ancestral/Omicron BA.1 bivalent booster mRNA vaccination. An Omicron BA.5 infection in addition to bivalent vaccination, led to a higher ratio of Omicron BA.5 to ancestral strain neutralization activity compared to no bivalent vaccination and no recent SARS‐CoV‐2 infection. In conclusion, SARS‐CoV‐2 T‐cell and antibody responses persist for up to 10 months after a monovalent booster mRNA vaccination. An ancestral/Omicron BA.1 bivalent booster mRNA vaccination increases these immune responses and also induces Omicron BA.5 cross‐neutralization antibody activity. Finally, our data indicate that hybrid immunity is associated with improved preservation of T‐cell immunity.