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April 23, 2026PEDIATRICS1 citations

SARS-CoV-2 Vaccination Before and During Pregnancy and Prevention of Infant COVID-19 Infection

KJKaren B. JacobsonKaiser Permanente MMMaqdooda Merchant BFBruce FiremanKaiser Permanente

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This research aims to determine how maternal SARS-CoV-2 vaccination before and during pregnancy affects COVID-19 infection rates in infants.
Observed infants born between July 1, 2021, and June 30, 2023, and categorized maternal vaccination status.
Examined vaccine effectiveness using Cox regression models to analyze COVID-19 cases and hospitalizations.
Conducted secondary analyses based on vaccination timing related to the pregnancy trimester.
Among 78,644 infants, 4.6% contracted COVID-19, with 0.1% hospitalized.
Vaccine effectiveness during pregnancy was 7.5% for preventing infection and 52.9% for preventing hospitalization.
Vaccination in the third trimester showed a 19.2% effectiveness against infection and 64.6% against hospitalization.

Resumen

BACKGROUND SARS-CoV-2 vaccination during pregnancy reduces COVID-19 risk in infancy. Whether maternal vaccination before pregnancy similarly protects infants against COVID-19 is unknown. METHODS We examined the effectiveness of maternal messenger RNA SARS-CoV-2 vaccination before and during pregnancy in preventing COVID-19 in infants aged 0–6 months born between July 1, 2021, and June 30, 2023, at Kaiser Permanente Northern California. Maternal vaccination status was categorized as vaccinated during pregnancy, during a prepregnancy interval (0–3, 3–6, 6–12, and 12 months prepregnancy), or unvaccinated. Secondary analyses examined the effectiveness of vaccination by trimester. COVID-19 was defined by positive SARS-CoV-2 PCR result or diagnostic code, and COVID-19–related hospitalizations were confirmed by medical record review. Vaccine effectiveness (VE) was examined by Cox regression models adjusted for maternal and infant characteristics, calculated as (1 − hazard ratio) × 100%. RESULTS Among 78 644 infants, 3648 (4.6%) had COVID-19 infection and 76 (0.1%) experienced COVID-19–related hospitalization before age 6 months. For the 4 prepregnancy vaccination intervals, estimates for VE against COVID-19 infection ranged from −14.9% (95% CI, −32.8% to 0.5%) for less than 3 months prepregnancy to 23.6% (−14.3% to 49%) for more than 12 months prepregnancy. VE anytime during pregnancy was 7.5% (−2% to 16.2%) against infant COVID-19 infection and 52.9% (11.1%–75.1%) against infant COVID-19–related hospitalization. Effectiveness of third-trimester vaccination was 19.2% (8.6%–28.6%) against infant COVID-19 infection and 64.6% (12.3%–85.7%) against infant COVID-19–related hospitalizations. CONCLUSION Maternal vaccination during the third trimester was protective against infant COVID-19 infections. Maternal vaccination during pregnancy, particularly during the third trimester, was effective against infant COVID-19–related hospitalizations. Vaccination before pregnancy did not protect infants.

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