Antibody Responses After a Single Dose of ChAdOx1 nCoV-19 Vaccine in Healthcare Workers Previously Infected with SARS-CoV-2

Background Recent reports demonstrate robust serological responses to a single dose of messenger RNA (mRNA) vaccines in individuals previously infected with SARS-CoV-2. Data on immune responses following a single-dose adenovirus-vectored vaccine expressing the SARS-CoV-2 spike protein (ChAdOx1 nCoV-19) in individuals with previous SARS-CoV-2 infection are however limited, and current guidelines recommend a two-dose regime regardless of preexisting immunity. Methods We compared spike-specific IgG and pseudo-neutralizing spike-ACE2 blocking antibodies against SARS-CoV-2 wild type and variants B.1.1.7, B.1.351, and P1 following two doses of the mRNA vaccine BNT162b2 and a single dose of the adenovector vaccine ChAdOx1 nCoV-19 in 232 healthcare workers with and without previous COVID-19. Findings The post-vaccine levels of spike-specific IgG and neutralizing antibodies against the SARS-CoV-2 wild type and all three variants of concern were similar or higher in participants receiving a single dose of ChAdOx1 nCoV-19 vaccine post SARS-CoV-2 infection (both < 11 months post infection (n=37) and ≥ 11 months infection (n=46)) compared to participants who received two doses of BNT162b2 vaccine (n=149). Interpretation Our data support that a single dose ChAdOx1 nCoV-19 vaccine serves as an effective immune booster after priming with natural SARS-CoV-2 infection up to at least 11 months post infection.