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HomeCoronavirus WatchEffectiveness of Pfizer vaccine in pregnancy — Clalit Health Services study

Effectiveness of Pfizer vaccine in pregnancy — Clalit Health Services study

The BioNTech-Pfizer vaccine has similar high vaccine effectiveness in pregnant women as to that in the general population, a study in Nature found.

To evaluate the effectiveness of the BioNTech-Pfizer (BNT162b2) messenger RNA vaccine in pregnant women, we conducted an observational cohort study of pregnant women aged 16 years or older, with no history of SARS-CoV-2, who were vaccinated between 20 December 2020 and 3 June 2021.

In this study, a total of 10,861 vaccinated pregnant women were matched to 10,861 unvaccinated pregnant controls using demographic and clinical characteristics. Study outcomes included documented infection with SARS-CoV-2, symptomatic COVID-19, COVID-19-related hospitalisation, severe illness and death. Estimated vaccine effectiveness from 7 through to 56 d after the second dose was 96% (95% confidence interval 89–100%) for any documented infection, 97% (91–100%) for infections with documented symptoms and 89% (43–100%) for COVID-19-related hospitalisation. Only one event of severe illness was observed in the unvaccinated group and no deaths were observed in either group.

In summary, the BNT162b2 mRNA vaccine was estimated to have high vaccine effectiveness in pregnant women, which is similar to the effectiveness estimated in the general population.

Study details

Effectiveness of the BNT162b2 mRNA COVID-19 vaccine in pregnancy

Noa Dagan, Noam Barda, Tal Biron-Shental, Maya Makov-Assif, Calanit Key, Isaac S. Kohane, Miguel A. Hernán, Marc Lipsitch, Sonia Hernandez-Diaz, Ben Y. Reis & Ran D. Balicer

Published in NatureMedicine on 7 September 2021

Abstract
To evaluate the effectiveness of the BNT162b2 messenger RNA vaccine in pregnant women, we conducted an observational cohort study of pregnant women aged 16 years or older, with no history of SARS-CoV-2, who were vaccinated between 20 December 2020 and 3 June 2021. A total of 10,861 vaccinated pregnant women were matched to 10,861 unvaccinated pregnant controls using demographic and clinical characteristics. Study outcomes included documented infection with SARS-CoV-2, symptomatic COVID-19, COVID-19-related hospitalisation, severe illness and death. Estimated vaccine effectiveness from 7 through to 56 d after the second dose was 96% (95% confidence interval 89–100%) for any documented infection, 97% (91–100%) for infections with documented symptoms and 89% (43–100%) for COVID-19-related hospitalisation. Only one event of severe illness was observed in the unvaccinated group and no deaths were observed in either group.

In summary, the BNT162b2 mRNA vaccine was estimated to have high vaccine effectiveness in pregnant women, which is similar to the effectiveness estimated in the general population.

As the number of vaccinated individuals increases worldwide, there is an opportunity to evaluate the real-world effectiveness and safety of the mRNA COVID-19 vaccines using observational data. Initial reports regarding vaccine safety indicate no obvious safety signals among pregnant women. However, information regarding vaccine effectiveness among pregnant women is still limited.

The immune system is known to undergo alterations during pregnancy. For example, there is evidence that levels of CD4+ and CD8+ lymphocytes decrease during pregnancy, as do the levels of some inflammatory cytokines. Because mRNA-based vaccines are a new technology that has not been widely tested in pregnant women, it is plausible that the immune response triggered by these vaccines in pregnant women may be altered compared to the general population, increasing the need to evaluate vaccine effectiveness specifically for this subpopulation. In a previous report, confidence in vaccine effectiveness among pregnant women was mentioned as one of the strongest predictors of COVID-19 vaccine acceptance in this group12.

The objective of this study was to estimate real-world vaccine effectiveness in a large observational cohort of pregnant women, aged 16 years or older, with no previous SARS-CoV-2 infection and recruited between 20 December 2020 and 3 June 2021. Vaccinated women were exactly matched to unvaccinated controls on a set of demographic and clinical characteristics and followed for a median of 77 d. Vaccine effectiveness was estimated in several follow-up periods for documented infection with SARS-CoV-2, symptomatic COVID-19, COVID-19-related hospitalisation, severe COVID-19 and COVID-19-related death.

Results
Of 38,836 women members of Clalit Health Services (CHS) vaccinated during pregnancy, 28,227 met the eligibility criteria; 10,861 of these vaccinated women were successfully matched to unvaccinated pregnant controls The full population was similar to the eligible population. Matched individuals were also similar to the eligible population, albeit with a lower lower prevalence of some risk factors for severe COVID-19

The baseline characteristics of the matched individuals were very similar in the vaccinated and unvaccinated. The median age was 30 years, with 26%, 48% and 26% of pregnancies in the first, second and third trimesters, respectively. Of the matched individuals, 18% had at least one risk factor for severe COVID-19, the most common being obesity.

During a median follow-up of 77 d, 131 infections were documented in the vaccination group and 235 infections in the control group. in the vaccinated and unvaccinated groups are similar until day 14, when incidence in the vaccinated group begins to decline sharply.

The estimated vaccine effectiveness for documented infections was 67% (95% confidence interval (CI) = 40–84%) in days 14–20 after the first dose, 71% (33–94%) in days 21–27 after the first dose and 96% (89–100%) in days 7–56 after the second dose (Table 1). The estimated vaccine effectiveness for symptomatic infection was 66% (95% CI = 32–86%) in days 14–20 after the first dose, 76% (30–100%) in days 21–27 after the first dose and 97% (91–100%) in days 7–56 after the second dose. Vaccine effectiveness for COVID-19-related hospitalisation was 89% (43–100%) in days 7–56 after the second dose.

Vaccine effectiveness could not be meaningfully estimated for the other outcomes and time periods due to the small number of events.

 

Nature article – Effectiveness of the BNT162b2 mRNA COVID-19 vaccine in pregnancy (Open access)

 

See more from MedicalBrief archives:

 

Mortality 20x higher in pregnant women with COVID but SAHPRA says no to vaccination

 

Unpacking COVID vaccination's effect on fertility and sexual functioning

 

Pregnant women pass COVID antibodies to their babies — Weill Cornell

 

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