ABSTRACT
Background: The purpose of this study was to evaluate whether a bivalent coronavirus disease 2019 (COVID-19) vaccine protects against COVID-19. Methods: The study included employees of Cleveland Clinic in employment when the bivalent COVID-19 vaccine first became available. Cumulative incidence of COVID-19 over the following 26 weeks was examined. Protection provided by vaccination (analyzed as a time-dependent covariate) was evaluated using Cox proportional hazards regression, with change in dominant circulating lineages over time accounted for by time-dependent coefficients. The analysis was adjusted for the pandemic phase when the last prior COVID-19 episode occurred and the number of prior vaccine doses. Results: Among 51 017 employees, COVID-19 occurred in 4424 (8.7%) during the study. In multivariable analysis, the bivalent-vaccinated state was associated with lower risk of COVID-19 during the BA.4/5-dominant (hazard ratio, 0.71 [95% confidence interval, .63-79]) and the BQ-dominant (0.80 [.69-.94]) phases, but decreased risk was not found during the XBB-dominant phase (0.96 [.82-.1.12]). The estimated vaccine effectiveness was 29% (95% confidence interval, 21%-37%), 20% (6%-31%), and 4% (-12% to 18%), during the BA.4/5-, BQ-, and XBB-dominant phases, respectively. The risk of COVID-19 also increased with time since the most recent prior COVID-19 episode and with the number of vaccine doses previously received. Conclusions: The bivalent COVID-19 vaccine given to working-aged adults afforded modest protection overall against COVID-19 while the BA.4/5 lineages were the dominant circulating strains, afforded less protection when the BQ lineages were dominant, and effectiveness was not demonstrated when the XBB lineages were dominant.
ABSTRACT
BACKGROUND: The purpose of this study was to evaluate whether boosting previously infected or vaccinated healthcare personnel with a vaccine developed for an earlier variant of SARS-CoV-2 protects against the Omicron variant. METHODS: Employees of Cleveland Clinic previously infected with or vaccinated against COVID-19, and working in Ohio the day the Omicron variant was declared a variant of concern, were included. The cumulative incidence of COVID-19 was examined over two months during an Omicron variant surge. Protection provided by boosting (analyzed as a time-dependent covariate) was evaluated using Cox proportional hazards regression. Analyses were adjusted for time since proximate SARS-CoV-2 exposure as a time-dependent covariate. RESULTS: Among 39 766 employees, 8037 (20%) previously infected and the remaining previously vaccinated, COVID-19 occurred in 6230 (16%) during the study. Risk of COVID-19 increased with time since proximate SARS-CoV-2 exposure, and boosting protected those >6 months since prior infection or vaccination. In multivariable analysis, boosting was independently associated with lower risk of COVID-19 among those vaccinated but not previously infected (HR, .43; 95% CI, .41-.46) as well as those previously infected (HR, .66; 95% CI, .58-.76). Among those previously infected, receiving 2 compared to 1 dose of vaccine was associated with higher risk of COVID-19 (HR, 1.54; 95% CI, 1.21-1.97). CONCLUSIONS: Administering a COVID-19 vaccine not designed for the Omicron variant, >6 months after prior infection or vaccination, protects against Omicron variant infection in those previously infected or vaccinated. There is no evidence of an advantage to administering more than 1 dose of vaccine to previously infected persons.
ABSTRACT
BACKGROUND: The aim was to evaluate the necessity of coronavirus disease 2019 (COVID-19) vaccination in persons with prior COVID-19. METHODS: Employees of the Cleveland Clinic working in Ohio on 16 December 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 receiving the second dose of COVID-19 mRNA vaccine. Cumulative incidences of COVID-19, symptomatic COVID-19, and hospitalizations for COVID-19 were examined over the next year. RESULTS: Among 52 238 employees, 4718 (9%) were previously infected and 36 922 (71%) were vaccinated by the study's end. Cumulative incidence of COVID-19 was substantially higher throughout for those previously uninfected who remained unvaccinated than for all other groups, lower for the vaccinated than unvaccinated, and lower for those previously infected than those not. Incidence of COVID-19 increased dramatically in all groups after the Omicron variant emerged. In multivariable Cox proportional hazards regression, both prior COVID-19 and vaccination were independently associated with significantly lower risk of COVID-19. Among previously infected subjects, a lower risk of COVID-19 overall was not demonstrated, but vaccination was associated with a significantly lower risk of symptomatic COVID-19 in both pre-Omicron (HR, .60; 95% CI, .40-.90) and Omicron (HR, .36; 95% CI, .23-.57) phases. CONCLUSIONS: Both previous infection and vaccination provide substantial protection against COVID-19. Vaccination of previously infected individuals does not provide additional protection against COVID-19 for several months, but after that provides significant protection at least against symptomatic COVID-19.