The efficacy of two injections of the SARS-CoV-2 spike mRNA vaccines (BNT162b2 [Pfizer] and mRNA-1273 [Moderna]) in preventing symptomatic SARS-CoV-2 infection in persons without previous COVID-19 has been shown to be high. In this article the authors wondered what the response would be to the first vaccine dose in persons with previous COVID-19. 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%] was assessed: 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) who received their first spike mRNA vaccine dose in 2020 (88 received the Pfizer vaccine and 22 the Moderna vaccine). SARS-CoV-2 spike IgG was measured with the use of a previously described two-step enzyme-linked immunosorbent assay and expressed as area under the curve (AUC). Repeated sampling after the first dose indicates that the majority of seronegative participants had variable and relatively low SARS-CoV-2 IgG responses within 9 to 12 days after vaccination (median AUC before vaccination, 1 [67 participants]; at 0 to 4 days, 1 [12 participants]; at 5 to 8 days, 1 [22 participants]; at 9 to 12 days, 439 [13 participants]; at 13 to 16 days, 1016 [18 participants]; at 17 to 20 days, 1037 [21 participants]; at 21 to 27 days, 1293 [19 participants]; and after the second dose, 3316 [36 participants]). In contrast, participants with SARS-CoV-2 antibodies at baseline before the first vaccine injection rapidly developed uniform, high antibody titers within days after vaccination (median AUC before vaccination, 90 [43 participants]; at 0 to 4 days, 133 [7 participants]; at 5 to 8 days, 14,208 [15 participants]; at 9 to 12 days, 20,783 [8 participants]; at 13 to 16 days, 25,927 [20 participants]; at 17 to 20 days, 11,755 [4 participants]; at 21 to 27 days, 19,534 [14 participants]; and after the second dose, 22,509 [19 participants]). The authors concluded that a single dose of mRNA vaccine elicited rapid immune responses in seropositive participants, with postvaccination antibody titers that were similar to or exceeded titers found in seronegative participants who received two vaccinations. Whether a single dose of mRNA vaccine provides effective protection in seropositive persons requires investigation.
Krammer F, et al. Antibody Responses in Seropositive Persons after a Single Dose of SARS-CoV-2 mRNA Vaccine. N Engl J Med. 2021 Mar 10. doi: 10.1056/NEJMc2101667.