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The rate of US newborns with maternal-transmitted COVID-19 was five times higher during Omicron variant predominance than before, according to a study led by researchers at the Centers for Disease Control and Prevention (CDC).

In the study, published today in Pediatrics, the researchers parsed data on infants aged 0 to 6 months born to COVID-infected mothers in 2020 or 2021 in six US jurisdictions reporting data to the CDC's Surveillance for Emerging Threats to Pregnant People and Infants Network.

Massachusetts, Minnesota, Missouri, Puerto Rico, Tennessee, and Philadelphia reported cases before (March 22, 2020, to December 18, 2021) and during (December 19, 2021, to September 9, 2022) Omicron predominance.

Before Omicron predominance, 27,403 infants were born to mothers who tested positive for COVID-19 (rate, 3.1 per 100 person-years). During the Omicron wave, 14,115 infants tested positive for COVID-19 (rate, 15.3 per 100 person-years; incidence rate ratio [IRR], 5.00).

The proportion of infants infected within 14 days after delivery by mothers infected within 14 days before delivery fell from 31.4% before to 0.8% during Omicron predominance, which the researchers said suggests that the higher rate of infection during Omicron wasn't caused by increased perinatal transmission.

In a subanalysis limited to infants born to infected mothers pre-Omicron, the IRR rose to 5.83. "This finding aligns with other evidence of reduced protection against Omicron from previous infection with other variants," the authors wrote. "Increased transmissibility of the Omicron variant to infants who are ineligible to receive COVID-19 vaccination, raises the importance of preventing SARS-CoV-2 transmission through other means, such as vaccination of pregnant and postpartum people."

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