Time Since SARS-CoV-2 Infection and Humoral Immune Response Following BNT162b2 mRNA Vaccination

Background: To optimise the use of available SARS-CoV-2 vaccines, some advocate delaying second vaccination for individuals infected within six months. We studied whether post-vaccination immune response is equally potent in individuals infected over six months prior to vaccination. Methods: We tested serum IgG binding to SARS-CoV-2 spike protein and neutralising capacity in 110 healthcare workers, before and after both BNT162b2 messenger RNA (mRNA) vaccinations. We compared outcomes between participants with more recent infection (n=18, median two months, IQR 2-3), with infection-vaccination interval over six months (n=19, median nine months, IQR 9-10), and to those not previously infected (n=73). Findings: Both recently and earlier infected participants showed comparable humoral immune responses after a single mRNA vaccination, while exceeding those of previously uninfected persons after two vaccinations with 2·5 fold (p=0·003) and 3·4 fold (p