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Updated: Jun 13, 2026

Induction of Maternal Immune Activation in Mice at Mid-gestation Stage with Viral Mimic Poly(I:C)
Published on: March 25, 2016
Effectiveness of maternal COVID-19 vaccination varies by gestational timing: results from a claims-based cohort
Stacey L Rowe1, Matthew M Coates2, Sheena G Sullivan3
1Kaiser Permanente.
Abstract:
We evaluated COVID-19 vaccine effectiveness (VE) during pregnancy by dose and trimester in a claims-based cohort of 414,909 pregnant women from 25 December 2020 to 16 September 2022. Vaccination was modeled as a time-varying exposure using weighted Cox proportional hazards models to estimate VE against medically-attended COVID-19 and COVID-19-related hospitalization. Overall, 58,975 (14.2%) women received ≥ 1 dose during pregnancy. We identified 39,202 COVID-19 cases, including 1,130 hospitalizations, with most outcomes (> 93%) occurring during unvaccinated person-time. VE against medically-attended COVID-19 was low-to-moderate across trimesters, with the highest estimates after late second trimester vaccination (36.3%, 95% CI: 26.9-44.4) or ≥ 2 doses (40.7%, 95% CI: 26.3-52.3). VE against hospitalization was higher, albeit with wider confidence intervals (late second trimester, 73.1%, 95% CI: 13.3-91.6). COVID-19 vaccination during pregnancy provided meaningful maternal protection, particularly against severe disease, with some indications that protection may be greatest when given during later gestational periods.
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