Infants less than 6 months of age are at risk of severe COVID-19 but are not yet eligible for vaccination. The best way to prevent COVID-19 in this age group is maternal vaccination.

Between July 1, 2021, and March 8, 2022, researchers at the Centers for Disease Control and Prevention (CDC) studied about 1,000 infants born to mothers who either had or had not been vaccinated during pregnancy (Halasa NB, Olson SM, Staat MA, et al. Maternal vaccination and risk of hospitalization for covid-19 among infants. New Engl J Med. 2022 July 14;387(2):109-119). These studies were performed in 30 hospitals across 22 states during a time when the delta and omicron variants were the most common circulating strains. About 16% of the case infants (infants hospitalized with COVID-19) and 29% of control infants (infants hospitalized without COVID-19) were born to mothers who had been fully vaccinated during pregnancy. Among the case infants, 21% required intensive care and 12% required mechanical ventilation. The effectiveness of maternal vaccination against hospitalization for COVID-19 was 52% — 80% during the delta period and 38% during the omicron period. Vaccine effectiveness was 69% when maternal vaccination occurred after 20 weeks of pregnancy and 38% when maternal vaccination occurred during the first 20 weeks of pregnancy. Two infants died from COVID-19 during the study; neither infant’s mother had been vaccinated.

The authors concluded, “Maternal vaccination with two doses of mRNA vaccine was associated with a reduced risk of hospitalization for COVID-19, including for critical illness, among infants younger than 6 months of age.”

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