Necessity of COVID-19 Vaccination in Persons who have Already had COVID-19
Abstract
Background
The purpose of this study was to evaluate the necessity of COVID-19 vaccination in persons with prior COVID-19.
Methods
Employees of Cleveland Clinic working in Ohio on Dec 16, 2020, the day COVID-19 vaccination was started, were included. Anyone who tested positive for COVID-19 at least once before the study start date was considered previously infected. One was considered vaccinated 14 days after receipt of the second dose of a COVID-19 mRNA vaccine. The cumulative incidence of COVID-19, symptomatic COVID-19, and hospitalizations for COVID-19, were examined over the next 10.5 months.
Results
Among the 52238 employees, 4718 (9%) had prior COVID-19 at the start of the study, and 35113 (67%) had received at least two doses of the vaccine by the end of the study. Of the 4284 COVID-19 infections during the study, 3476 (81.1%) occurred in persons who were unvaccinated, and 4263 (99.5%) occurred among those without prior COVID-19. In Cox proportional hazards regression, both prior COVID-19 and vaccination were independently associated with significantly lower risk of COVID-19. Vaccination was associated with lower risk of COVID-19 among those without prior COVID-19 (HR 0.24, 95% CI 0.22–0.26) but not among those with prior COVID-19 (HR 0.86, 95% CI 0.33–2.29).
Conclusions
Both previous infection and vaccination provide substantial protection against COVID-19. Vaccination reduces risk of COVID-19 among those without prior COVID-19 but not among those with prior COVID-19, at least not within one year following infection.
Summary
Cumulative incidence of COVID-19 over 10.5 months, including the Delta phase, was examined among 52238 employees at Cleveland Clinic. Vaccination was associated with significantly lower risk of COVID-19 among those without prior COVID-19 but not among those with prior COVID-19.
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