A new study on COVID-19's effects on US infants notes that the proportion of hospitalized babies of mothers vaccinated during pregnancy plunged from 18% in October 2023 to 4% in April 2024, underscoring the need for increased vaccine uptake.
And another report estimates that unexpected infant deaths jumped as much as 14% in 2021 relative to prepandemic totals.
Infants depend on maternal antibodies
Yesterday in Morbidity and Mortality Weekly Report (MMWR), a team led by Centers for Disease Control and Prevention (CDC) researchers analyzed COVID-19–Associated Hospitalization Surveillance Network (COVID-NET) data on 1,470 COVID-19 hospitalizations among infants younger than 6 months, outcomes, maternal vaccination status, and viral codetections from October 2022 to April 2024.
Infants aged <6 months are at increased risk for severe COVID-19 disease but are not yet eligible for COVID-19 vaccination; these children depend upon transplacental transfer of maternal antibody, either from vaccination or infection, for protection.
During the study period, weekly COVID-19 hospitalization rates among infants were higher than those of any other age-group, except adults aged 75 years and older, and were comparable to rates among those aged 65 to 74. Hospitalization rates among young infants peaked at 23.0 and 20.3 per 100,000 infants in December 2022-23 and January 2023-24, respectively.
"Infants aged <6 months are at increased risk for severe COVID-19 disease but are not yet eligible for COVID-19 vaccination; these children depend upon transplacental transfer of maternal antibody, either from vaccination or infection, for protection," the study authors wrote.
Of 1,065 infants with known maternal vaccination status, 87.5% of moms had no documentation of COVID-19 vaccination during pregnancy. The proportion of hospitalized infants whose mothers had received COVID-19 vaccines during pregnancy was 17.6% in 2022-23, falling to 4.3% in 2023-24.
Excluding newborns hospitalized at birth, roughly 1 in 5 infants younger than 6 months and hospitalized for COVID-19 were admitted to an intensive care unit (ICU), 1 one in 20 needed mechanical ventilation, and 9 died in the hospital. All infants who died had unvaccinated mothers.
Of 999 (87.1%) hospitalized infants tested for other viruses, one or more other viruses were identified in 286 (29.7%), including 19.3% with respiratory syncytial virus (RSV), 12.2% with rhinovirus/enterovirus, and 1.9% with influenza. Among 233 of 260 infants (89.8%) admitted to an ICU and tested for other pathogens, another virus was identified in 41.2%, including 25.1% with RSV.
"To protect young infants from severe COVID-19–associated outcomes, prevention should focus on vaccination of pregnant persons, which protects infants through transplacental transfer of antibodies, and nonpharmaceutical interventions, such as hand hygiene and avoiding exposure to persons with respiratory illness signs and symptoms," the researchers wrote.
Pandemic rise of sudden infant death
For the second study, published yesterday in JAMA Network Open, a Penn State–led research team compared monthly rates of sudden unexpected infant death (SUID) and sudden infant death syndrome (SIDS) during the COVID-19 pandemic (March 2020 to December 2021) with those from before the pandemic (March 2018 to December 2019). The investigators used CDC data on infant deaths from SIDS, unknown causes, and accidental suffocation and strangulation in bed.
SIDS, a kind of SUID that occurs during sleep and has no known cause, makes up about a third of SUID cases.
"Infection has been postulated as a driver in the sudden infant death syndrome (SIDS) cascade," the researchers wrote. "Epidemiologic patterns of infection, including respiratory syncytial virus and influenza, were altered during the COVID-19 pandemic."
From January 1, 2018, to December 31, 2021, 14,308 infants (42% girls) died of SUID. The risk of SUID rose slightly during the pandemic (intensity ratio [IR], 1.06) and increased beyond prepandemic numbers starting in July 2020, rising 10% to 14% from June to December 2021.
These findings support the hypothesis that off-season resurgences in endemic infectious pathogens may be associated with SUID rates, with RSV rates in the US closely approximating this shift.
Rates of SIDS were higher than baseline throughout the pandemic period, with the biggest spike in July 2021 (IR, 1.18) and August 2021 (IR, 1.17). Seasonal shifts in hospitalizations for RSV coincided with monthly changes in SUID in 2021.
"These findings support the hypothesis that off-season resurgences in endemic infectious pathogens may be associated with SUID rates, with RSV rates in the US closely approximating this shift," the authors concluded. "Further investigation into the role of infection in SUID and SIDS is needed."
In a Penn State press release, first author Emma Guare, a fourth-year medical student at Penn State, said SUID likely has many causes. "Even with education about safe sleep environments and the back-to-sleep campaign encouraging parents to put babies to sleep on their backs, there's still a high rate of SUID," she said.
Coauthor Erich Batra, MD, of Penn State, said no one knows why some babies are vulnerable to SUID or SIDS. "It could be that infections like RSV amplify those factors and make them more vulnerable,” he said. "With RSV in particular, there have been questions about whether RSV causes more apnea, when you stop breathing temporarily, than other viruses and if that contributes to an environment conducive to SUID."
