COVID-19 Disease Incidence and Severity in Persons Previously Infected and Unvaccinated vs Previously Uninfected and Vaccinated.

Abstract

Using the national COVID-19 database of the US Department of Veterans Affairs, we matched pairs of individuals who were previously uninfected and vaccinated (≥2 doses of an mRNA vaccine) and previously infected and unvaccinated. The incidence rate of breakthrough infection among vaccinated individuals (per 1000 person-days, 0.30; 95% CI, .29-.32) was similar to the reinfection rate among unvaccinated individuals (0.31; 95% CI, .30-.32; P = .5). The incidence rate of hospitalization/death was higher after reinfection (7.31; 95% CI, 6.66-8.03) as compared with the rate after breakthrough infection (4.69; 95% CI, 4.06-5.42; P < .0001). The incidence of hospitalization/death is significantly higher after reinfection among unvaccinated individuals as compared with breakthrough infection after vaccination.