Infant SARS-CoV-2 infection five times more likely during omicron

Key takeaways:

• Infants born to pregnant people with SARS-CoV-2 during pregnancy were five times as likely to test positive during omicron.
• It increased to six times higher when the pregnant person had SARS-CoV-2 before omicron.

Infants born to people infected with SARS-CoV-2 during pregnancy were five times as likely to test positive for the virus from age 0 to 6 months during the omicron period than previous waves, according to research published in Pediatrics.

According to Lucas Gosdin, PhD, MPH, an Epidemic Intelligence Service officer in the CDC’s Division of Birth Defects and Infant Disorders, previous analyses showed a low incidence of SARS-CoV-2 infection among infants born to people infected with the coronavirus during pregnancy.

“However,” Gosdin told Healio, “given that the omicron variant is more transmissible and infants up to 6 months old are the only group with no authorized COVID‐19 vaccine, we sought to understand the rates of infant infection during the period of omicron variant predominance compared to the previous period.”

Gosdin and colleagues collected laboratory data from Minnesota, Massachusetts, Missouri, Puerto Rico, Tennessee and the city of Philadelphia on pregnant people with SARS-CoV-2 during pregnancy and their infants through 6 months of age from March 22, 2020, to Dec. 18, 2021 — the period before omicron predominance — and from Dec. 19, 2021 to Sept. 9, 2022, when omicron predominated. The researchers then calculated incidence rates for each period.

“To understand how maternal infection with a previous variant could impact the risk of infant infection with the omicron variant, we repeated this method limited to a subset of infants born to people who had COVID‐19 before the omicron variant was widespread,” Gosdin said.

They found that among 27,403 pregnant patients with SARS-CoV-2 during the period before omicron predominance, the incidence of positive tests among infants aged 0 to 6 months was 3.1 per 100 person-years. That rate climbed to 15.3 per 100 person-years (incidence rate ratio = 5; 95% CI, 4.83-5.21) among 14,115 pregnant patients with SARS-CoV-2 during omicron.

The rate of infection was about six times higher when the pregnant person had SARS-CoV-2 before omicron, suggesting that infants are less protected from being infected with the omicron variant when the pregnant person’s infection was from a previous variant.

“We also found that the proportion of infants infected within 14 days after delivery with maternal infections within 14 days before delivery declined during the omicron,” Gosdin said. “This indicates that the increased rate of infection during the omicron period was not due to increased transmission from the pregnant person to the infant around the time of delivery.”

The increase, Gosdin said, mirrors those observed in the general population and is consistent with increases in infant hospitalizations during the omicron period.

“Even if a pregnant person previously had COVID‐19, they should still take steps to protect themselves and their infants from COVID‐19 and stay up to date with their COVID‐19 vaccines,” Gosdin said.

He added that people with COVID‐19 during pregnancy are more likely to deliver a preterm or stillborn infant and may also be more likely to have other pregnancy complications.

“COVID‐19 vaccination during pregnancy helps prevent severe illness and death in people who are pregnant and protect babies younger than 6 months old from hospitalization caused by COVID‐19,” Gosdin said.