Helen Branswell , 2025-05-08 18:49:00
A new report from the Centers for Disease Control and Prevention shows there was a substantial drop in hospitalizations for respiratory syncytial virus this winter among very young children, who are at the highest risk of becoming severely ill if they contract RSV.
This past winter was the first during which new options for protecting babies from the virus became widely available in the United States, though the products were first introduced in a limited way in advance of the 2023-2024 season.
The study, published in the CDC’s online journal Morbidity and Mortality Weekly Report, cannot prove that the new tools are the reason for the drop in hospitalizations among children under 7 months old, the age group targeted for these interventions. But a rise in hospitalizations among slightly older children — still at risk but too old to be eligible for the products — shows the decline occurred in the context of a severe RSV season.
RSV is the No. 1 cause of hospitalizations of infants, with seriously ill babies struggling to breathe.
The new tools are a vaccine, made by Pfizer, that is offered to pregnant people in their third trimester if they are due to deliver between September and January, and an injection of monoclonal antibodies, made by Sanofi and AstraZeneca, which should be given at or near birth to babies whose mothers were not vaccinated, or near the start of the RSV season for babies who were born in the spring or summer. Infants should benefit from one or the other, but do not need both.
The vaccine, sold as Abrysvo, generates antibodies that are passed to the baby in the womb, giving protection during the first months of life. The antibody injection, sold under the name Beyfortus, is also given to some children entering their second RSV season, if they are considered at high risk of serious illness if they contract RSV.
“Although we need to do more, we know now that we can dramatically lower hospitalization rates due to severe RSV disease in young infants using our new tools — monoclonal antibodies and maternal immunization,” said one of the authors, Janet Englund, a professor of pediatrics at the University of Washington.
These products are believed to have the potential to dramatically reduce the toll RSV takes on infants, their families, and health care systems that can become overwhelmed during RSV season.
A number of publications from Europe, where the products were introduced earlier, have shown substantial reductions in severe RSV disease, especially in places where a high percentage of infants are protected.
In this study, scientists from the CDC and a number of academic institutions looked at data from two different surveillance networks, comparing hospitalizations this past winter to those that occurred during the two RSV seasons that preceded the Covid-19 pandemic, 2018-2019, and 2019-2020.
They saw a decline of between 45% and 52% in RSV hospitalizations of infants ages 0 to 2 months, when compared to the earlier years. When data from Houston were removed from one of the datasets, the decline in this age group was actually 71%. The RSV season in Houston began in September, before the product rollouts began.
“The goal of the study was to … see if these products made a difference — they did,” said Natasha Halasa, a professor of pediatrics at Vanderbilt University, and a co-author of the paper. “The findings from this study indicates that we are on the right path in reducing the risk of RSV hospitalizations in infants.”
When data for all children ages 0 to 7 months were included, the reduction was between 28% and 43%.
The researchers did not know what percentage of the babies in these two cohorts had been protected, either by receiving the monoclonal injection or because they received vaccine-induced antibodies in the womb, so they could not calculate how effective the products were in protecting the individual children.
Rollout of these products has been challenging, especially the antibody injection. Though it is covered by insurance and by the CDC’s Vaccines for Children program, it is expensive for birthing hospitals and pediatricians to stock, creating a situation where some might opt to let the other provide this service.
Halasa said more work is ongoing to identify the barriers to getting all babies protected, either via maternal vaccination or an antibody injection. “The goal is: Let’s get this in every baby we can,” she said in an interview.
