Immunization with nirsevimab (Beyfortus) was 90% effective in preventing infants from being hospitalized with respiratory syncytial virus (RSV), according to a new report led by the Centers for Disease Control and Prevention (CDC).
“This finding supports current CDC recommendations that all infants should be protected by maternal RSV vaccination or infant receipt of nirsevimab, to reduce the risk for RSV-associated hospitalization in their first RSV season,” authors wrote.
RSV causes about 50,000 to 80,000 hospitalizations and 100 to 300 deaths per year in children under 5 years, according to the CDC. Infectious disease experts hailed the August 2023 approval of nirsevimab as a major advancement to protect the youngest children.
Researchers set out to see if the monoclonal antibody would perform as well in a real-world setting as it did in clinical trials. They evaluated 699 infants hospitalized with acute respiratory illness from October 2023 through February 2024. About 1% of those who tested positive for RSV had received nirsevimab at least a week prior to developing symptoms, while 18% of those with a negative RSV test had received nirsevimab. The median time from immunization to symptom onset was 45 days.
The finding of 90% effectiveness post approval supports the clinical trials and pooled prelicensure data effectiveness studies that found nirsevimab to be 79% effective in reducing the risk of medically attended lower respiratory tract infection caused by RSV and 81% effective against hospitalization through six months after injection. Because antibodies wane over time, authors said effectiveness during a full season likely would be lower than what they found through February.
Nirsevimab is recommended for infants under 8 months during their first RSV season and high-risk toddlers 8-19 months. However, the first season of using the product was fraught with supply issues that kept some from being able to access it.
CDC data through January from just over 40 city and state jurisdictions show coverage for infants under 8 months ranged from 1.6% in Florida to 21.6% in Alaska. In a CDC telephone survey of just over 500 women with an infant under 8 months, 41% said their infant received nirsevimab and 22% said their infant definitely would receive it.
In September 2023, health officials approved a maternal RSV vaccine and said most infants whose mother received this vaccine would not need additional protection from nirsevimab. About 17.5% of eligible pregnant people had been vaccinated as of Jan. 31.
In February, manufacturer Sanofi announced pediatricians will be able to reserve doses of nirsevimab for the 2024-’25 season. The program will apply to private purchases of the monoclonal antibody. Sanofi also is expanding its manufacturing network in hopes of mitigating the supply issues that plagued this season’s launch.
Resources
- Information from the CDC on using nirsevimab
- Information on Sanofi’s reservation program for nirsevimab
- AAP RSV resources, including information on ordering, dosing, coding and a visual guide for nirsevimab administration
- AAP News article “How to use new CPT codes for administration of RSV immunizations”
- Vaccines for Children program operations guide addendum for nirsevimab
- Information for parents from HealthyChildren.org on RSV symptoms and when to call a doctor
- Pediatrics in Review article “Implications of Food and Drug Administration Approval of Respiratory Syncytial Virus Prophylactic Medications”
