Necessity of Coronavirus Disease 2019 (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 receiving 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 year. Results Among 52238 employees, 4718 (9%) were previously infected, and 36922 (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 the pre-Omicron (HR 0.60, 95% CI 0.40–0.90) and Omicron (HR 0.36, 95% CI 0.23–0.57) 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.

Coronavirus Disease 2019 (COVID-19) Vaccine Boosting in Persons Already Protected by Natural or Vaccine-Induced Immunity

“…This study corroborates findings from earlier studies that natural immunity from prior infection is more robust than immunity acquired through vaccination [11,17,18], and additionally finds that individuals previously infected with COVID-19 retain substantial protection against the Omicron variant for at least 6 months in the absence of vaccination. For those with waning natural or vaccine-induced immunity (6 months or more after prior infection or vaccination), boosting with a vaccine designed for an earlier variant of COVID-19 still provides significant protection against infection with the Omicron variant.…”

“…The explanation for this seeming anomaly is unlikely to be that people transiently lose vaccine-induced immunity after 3 months and regain it after 9 months. This finding could possibly be explained by the fact that those whose POIC occurred 9-12 months previously were those who would have faced the Delta variant within the preceding 3 months with waning vaccine-induced immunity (being past 6 months from their original vaccination) [11], and many of whom may have been inadvertently boosted by an unrecognized asymptomatic or pauci-symptomatic infection with the Delta variant. Those who were vaccinated 3-6 and 6-9 months prior to the start of this study would have been within 6 months of their vaccination during the Delta variant surge, thereby protected from a Delta variant infection at the time [11,16], and thus would not have had the benefit of a boost to their immunity from a Delta variant infection.…”

“…Individuals were considered boosted 7 days after receipt of a qualifying vaccine booster. Covariates collected were age, aggregated job title (to maintain anonymity for rare job titles), job location, and job type categorization into patient-facing or non-patient facing, as described in an earlier study [11]. Protected health information identifiers were not included in the extracted data, and institutional data governance rules related to employee data limited our ability to supplement our dataset with additional clinical variables.…”

Emergence of SARS-CoV-2 Omicron (B.1.1.529) variant, salient features, high global health concerns and strategies to counter it amid ongoing COVID-19 pandemic

“…It showed the effectiveness of boosting strategies in immunocompromised groups including cancer patients ( Zeng et al, 2021 ). In multivariable Cox proportional hazards regression analysis in the previously infected subjects, significant lower risk of infection with Omicron was not demonstrated but in vaccinated individuals it was reported ( Shrestha et al, 2022 ).…”

Antibody Response to SARS-CoV-2 Infection and Vaccination in COVID-19-naïve and Experienced Individuals

“…Clinical studies have raised the question of the utility of vaccinating CE individuals within the first 6 months after infection, as infection rates and hospitalizations in CE individuals have been observed to be lower than in vaccinated, CN persons [51,52]. Our data emphasize that at least one vaccine dose in CE individuals increases antibody and neutralization titers by 50-and 27-fold, respectively (Figures 1 and 4), that a second antigen exposure is required to elicit a detectable neutralization titer in some individuals (Figure 4), and that it greatly improves the correlation between antibody levels and neutralization (Figure 5).…”