Abstract
Preexisting immunity cross-reactive to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in SARS-CoV-1 survivors suggests that a coronavirus disease 2019 vaccine may boost such preexisting cross-reactive memory T cells. We measure SARS-CoV-2 and SARS-CoV-1 spike-specific neutralizing antibody and T cell responses in a single dose of Ad5-nCoV-immunized SARS-CoV-1 survivors 6 months after vaccination. Compared with Ad5-nCoV-immunized naive healthy individuals (NHIs), vaccination of Ad5-nCoV in SARS-CoV-1 survivors boosts the antibody response against SARS-CoV-1 but induces a limited neutralizing antibody that is capable of neutralizing SARS-CoV-2 variants of concern, and nearly all serum samples lose neutralization to Omicron subvariants. Immunized SARS-CoV-1 survivors produce a T cell response to SARS-CoV-2 comparable with that of Ad5-nCoV-immunized NHIs. However, a robust cross-reactive T cell response to SARS-CoV-1 is identified in immunized SARS-CoV-1 survivors compared with Ad5-nCoV-immunized NHIs. These findings suggest that vaccination with Ad5-nCoV elicits a stronger neutralizing antibody and cross-reactive T cell responses against SARS-CoV-1 in SARS-CoV-1 survivors.