1. In a retrospective cohort of Singaporean, maternal mRNA SARS-CoV-2 vaccination during pregnancy was associated with a 41.5% reduction in SaR-CoV-2 infection for infants aged 6 months or less.
2. Vaccination during pregnancy demonstrated a larger risk reduction for infants than vaccinations administered prior to pregnancy.
Evidence Rating Level: 2 (Good)
Analysis of population data suggests that infants aged 6 months or younger face an increased risk of severe SARS-CoV-2 infection compared to other age groups, representing a significant portion of COVID-19 hospitalizations during the Omicron-dominant waves. Maternal vaccination has been proposed as a preventative measure to prevent severe infections in newborns, though there continues to be a scarcity of evidence examining the optimal timing of vaccination and its efficacy in preventing severe Omicron XBB variant COVID-19 infections. This retrospective cohort study, spanning January 1, 2022, to March 31, 2023, sourced information from the official Singapore Ministry of Health databases to investigate this knowledge gap, specifically identifying infants up to 6 months of age. Maternal vaccination status was categorized into unvaccinated, vaccinated prior to pregnancy, and vaccinated during pregnancy. Inverse probability weighting addressed confounding factors, and Cox regressions estimated hazard ratios of SARS-CoV-2 infections and a vaccine effectiveness (VE) score was also calculated. Of 7,292 infants, maternal mRNA SARS-CoV-2 vaccination during pregnancy was associated with a 41.5% (95% CI, 22.8%-55.7%) reduction in SARS-CoV-2 infection risk. Notably, vaccination including a third dose (booster) during pregnancy demonstrated a significant 44.4% (95% CI, 26.2%-58.1%) VE, while vaccination prior to pregnancy showed only a 15.4% (95% CI, −17.6% to 39.1%) reduction. Infants born to mothers who received a third dose (booster) during pregnancy exhibited a VE of 76.7% (95% CI, 12.8%-93.8%) against the Omicron XBB variant. Notably however, the study was limited in that it did not analyze breastfeeding data, and hospitalization guidelines during the study period varied throughout. Nonetheless, there appears to be a protective impact of maternal mRNA SARS-CoV-2 vaccination during pregnancy to prevent severe Omicron XBB variant COVID-19 infections. This may help further inform prenatal vaccination counseling to optimize protection for newborns.
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