The efficacy of two injections of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike messenger RNA (mRNA) vaccines (BNT162b2 [Pfizer] and mRNA-1273 [Moderna])1 in preventing symptomatic SARS-CoV-2 infection in persons without previous coronavirus disease 2019 (Covid-19) has been shown to be high.2,3 We wondered what the response would be to the first vaccine dose in persons with previous Covid-19.

We took advantage of our ongoing institutional review board–approved, longitudinal PARIS (Protection Associated with Rapid Immunity to SARS-CoV-2) study to provide a limited snapshot of the antibody responses in 110 study participants with or without documented preexisting SARS-CoV-2 immunity (mean age overall, 40.0 years [range, 24 to 68; ≥60 years, 8%]; 67 seronegative participants [64% female] with a mean age of 41.3 years and 43 seropositive participants [59% female] with a mean age of 41.4 years) (Table S1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org) who received their first spike mRNA vaccine dose in 2020 (88 received the Pfizer vaccine and 22 the Moderna vaccine).