Researchers investigate potential link between RSV and sudden unexpected infant deaths

A rise in rates of sudden unexpected infant deaths may have been linked to an off-season surge of respiratory syncytial virus (RSV) in 2021, according to a new study published Thursday in the journal JAMA Open Network.

Sudden unexpected infant deaths (SUID) includes deaths of infants under one year old without a known cause, deaths that are due to accidental suffocation or strangulation in bed and those from sudden infant death syndrome (SIDS), according to the Centers for Disease Control and Prevention (CDC).

"This is an important topic because SIDS and other unexpected deaths are still one of the leading causes of infant mortality, and there's still a lot unknown," said Dr. John Brownstein, an epidemiologist and chief innovation officer at Boston Children's Hospital and an ABC News contributor.

The most recent CDC data shows about 3,700 infants died from SUID in 2022 and 41% were from SIDS.

"There are very few things that are as horrific as a family experiencing a sudden infant death, and especially given the causes are so often unknown," Brownstein said.

Using records from the CDC, researchers analyzed more than 14,000 cases of SUID and found that rates per 100,000 live births increased by 10% from 2019 to 2021.

Results showed the risk of SUID was highest from June to December 2021 -- at the same time there was an off-season surge in hospitalizations due to RSV after the virus skipped its typical winter season in 2020.

Influenza hospitalizations were rare during this time and hospitalizations from COVID-19 did not have any clear association with monthly changes in SUID rates in the study.

These findings may indicate a connection between the risk of SUID and seasonal shifts in infections like RSV, but more research is needed to better understand this link.

"The findings underscore the importance of monitoring infant mortality during and after pandemics and obviously it puts big support for vaccinations and RSV prevention," Brownstein said.

Currently, there are newer RSV shots available that doctors say are important to help prevent RSV and give babies the best protection against this virus that hospitalizes thousands of kids a year, mostly babies.

The American College of Obstetricians and Gynecologists recommends pregnant women get an RSV vaccine between 32 and 36 weeks of pregnancy to pass on antibody protection to newborns.

The CDC recommends an RSV antibody shot called nirsevimab for all babies less than 8 months old unless their mother received an RSV vaccine in pregnancy at least 2 weeks before birth.

While nirsevimab had supply constraints last year in its first season, Sanofi, the drug manufacturer, recently announced they have started shipping shots to doctors' offices and anticipate having enough doses for all eligible babies in the US this RSV season.

Doctors say safe sleep is also important for SUID prevention. The American Academy of Pediatrics recommends that infants sleep alone, placed down on their back on a firm, flat surface, with nothing in the sleeping area other than a fitted sheet.

Scott Gummerson, MD, ScM, is an emergency medicine resident and member of the ABC Medical News Unit.

Jade A. Cobern, MD, MPH is a physician board-certified in pediatrics and preventive medicine and a medical fellow of the ABC News Medical Unit.