COVID-19 Pandemic
Relative immune protection from combinations of prior infection and vaccination on incident SARS-CoV-2 infection/reinfection: a prospective cohort study comparing self-reported and antibody-based indicators of prior infection, February 2021 to January 2023 Ashley Judge* Ashley Judge Erika Beidelman David Allison Stephanie Dickenson Lilian Golzarri Arroyo Anna Macagno Jon Macy Kevin C. Maki Molly Rosenberg Christina Ludema
Both natural infection and vaccination provide immune protection from future SARS-CoV-2 infections. Better understanding the relative immunity conferred from acquired and vaccine-induced immunity in combination will be helpful in building a stronger evidence base for policy decisions. We assessed the relative effectiveness of combinations of vaccination and prior infection on risk of SARS-CoV-2 infection/reinfection with correction for possible exposure misclassification of prior infection by comparing prior infection operationalized as 1) documented prior infection and 2) documented prior infection and nucleocapsid receptor-binding antibody indication of prior infection. We used extended cox regression with robust standard errors to estimate the association between time-varying number of vaccine doses and time invariant prior infection on risk of infection/re-infection among a prospective cohort of US adults between February 2021 to January 2023, accounting for censoring with inverse probability of censoring weights. N=1905 adults contributed 398,126 person-days of observation. Relative to the unvaccinated with no prior infection, those with documented prior infections had a relative efficacy of 45.5% (95% CI: 8.0-67.7%) against infection/reinfection. For those with three vaccine doses and no prior infection, the relative efficacy of 58.0% (37.3%-71.8%). Similar relative efficacy estimates were observed after correction for prior infection status in the nearly 17% of those without documentation of prior infection who had nucleocapsid antibody levels as high or higher than levels beyond the first quartile of documented cases. Three vaccine doses without prior infection provided substantial protection against infection/reinfection as did naturally acquired immunity without vaccination in a cohort of adults primarily infected/reinfected during the Omicron variant. Correcting for prior infection reporting error did not impact results.
