With the COVID-19 pandemic ongoing, accurate assessment of population immunity and the effectiveness of booster and enhancer vaccine doses is critical. We compare COVID-19-related hospitalization incidence rates in 2,412,755 individuals across four exposure levels: non-recent vaccine immunity (two BNT162b2 COVID-19 vaccine doses five or more months prior), boosted vaccine immunity (three BNT162b2 doses), infection-induced immunity (previous COVID-19 without a subsequent BNT162b2 dose), and enhanced infection-induced immunity (previous COVID-19 with a subsequent BNT162b2 dose). Rates, adjusted for potential demographic, clinical and health-seeking-behavior confounders, were assessed from July-November 2021 when the Delta variant was predominant. Compared with non-recent vaccine immunity, COVID-19-related hospitalization incidence rates were reduced by 89% (87–91%) for boosted vaccine immunity, 66% (50–77%) for infection-induced immunity and 75% (61–83%) for enhanced infection-induced immunity. We demonstrate that infection-induced immunity (enhanced or not) provides more protection against COVID-19-related hospitalization than non-recent vaccine immunity, but less protection than booster vaccination. Additionally, our results suggest that vaccinating individuals with infection-induced immunity further enhances their protection.
Background: As mass vaccination campaigns against COVID-19 accelerate worldwide, there remains only limited evidence regarding vaccine effectiveness (VE) among pregnant women. Pregnant women have been shown to be at risk for severe COVID-19, resulting in adverse obstetrics outcomes, and their immune system is known to undergo alterations during pregnancy. Phase III clinical trials of the approved mRNA COVID-19 vaccines excluded pregnant women, yet current guidelines encourage offering the vaccine to pregnant women. In this study, we examine data from Israel’s largest healthcare organization to evaluate the effectiveness of the BNT162b2 mRNA vaccine among pregnant women. Methods: We conducted an observational cohort study of pregnant women 16 years or older, with no history of SARS-CoV-2, who were vaccinated between December 20, 2020 and June 3, 2021. Vaccinated subjects were matched to unvaccinated controls according to a set of demographic and clinical characteristics. Study outcomes included documented infection with SARS-CoV-2, symptomatic COVID-19, COVID-19-related hospitalization, severe illness and death. For each outcome, VE was estimated at several periods following vaccination as one minus the risk ratio using the Kaplan–Meier estimator. Results: 10,861 vaccinated women were matched to an identical number of unvaccinated controls. Estimated VE from 7 through 28 days after the second dose was 97% (95% CI 91%-100%) for any documented infection, 96% (86-100%) for infections with documented symptoms, and 85% (32%-100%) for COVID-19-related hospitalization. Only one event of severe illness was observed in the unvaccinated group, and no deaths were observed in either group -- insufficient incidence for estimating VE for these outcomes. Discussion: The BNT162b2 mRNA vaccine was found to have high VE among pregnant women. Since high VE has been reported as one of the strongest predictors of COVID-19 vaccine acceptance among pregnant women, the high VE estimates found in this study have the potential to increase vaccine acceptance in this group. In addition, the present VE estimates are similar to those reported in the general population for the same variants, suggesting that it may be possible to infer the VE for pregnant women from studies in the general population for both current and future variants.
Introduction:
With the COVID-19 pandemic ongoing, accurate assessment of population immunity and the effectiveness of booster and enhancer vaccines is critical.
Methods
We compare COVID-19-related hospitalization incidence rate ratios, adjusted for potential demographic, clinical and health-seeking-behavior confounders, in 2,412,755 individuals (235,552,274 person-days), across four exposures: 2 BNT162b2 doses, 5 or more months prior ("non-recent vaccine immunity"); 3 BNT162b2 doses (“boosted vaccine immunity”); previous COVID-19, with or without a subsequent BNT162b2 dose (“natural immunity” and “enhanced natural immunity” respectively).
Results
Compared with non-recent vaccine immunity, COVID-19-related hospitalization incidence rate ratios are 11% (9%-13%) for boosted vaccine immunity, 34% (23%-50%) for natural immunity and 25% (17%-39%) for enhanced natural immunity.
Conclusion
We demonstrate that natural immunity (enhanced or not) provides better protection against COVID-19-related hospitalization than non-recent vaccine immunity, but less protection than that attained from booster vaccination. Additionally, our results suggest that vaccinating individuals with natural immunity further enhances their protection.
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