New RSV vaccine 90% effective at preventing infant hospitalizations

Nirsevimab was approved in July 2023 and is already causing fewer infants to have severe cases of RSV.
This electron microscope image provided by the National Institutes of Health shows human RSV.
Posted at 12:45 PM, Mar 08, 2024

New Centers for Disease Control and Prevention data is showing that newly released RSV vaccines are highly effective at keeping infants from becoming hospitalized. 

The CDC says nirsevimab was 90% effective at preventing RSV-associated hospitalization in infants during their first RSV season. Nirsevimab was approved for babies and toddlers in July 2023.

The real-world usage of nirsevimab so far has outperformed data from clinical trials. Prior to its release, officials said nirsevimab reduced the risk of hospitalizations related to RSV among infants by 70%-75%. 

"The current RSV season is the first time nirsevimab was available to protect infants from severe RSV, so the data released today are the first United States estimates of nirsevimab effectiveness in protecting infants against RSV-related hospitalization in their first season of potential exposure to the virus," the CDC said. 

The study looked at 699 infants from October 2023 through February 2024. CDC officials did caution that its overall effectiveness may be lower once a full RSV season is complete. Generally, RSV activity declines in late March.

According to the CDC, RSV causes 58,000 hospitalizations annually among children under age 5.

CDC: 128 pregnant people and 25 infants received the wrong RSV shot
Someone with gloves holds RSV test kit.

CDC: 128 pregnant people and 25 infants received the wrong RSV shot

Although no serious harm or adverse reactions have been reported from the errors, the CDC emphasizes caution when administering the shots.


The CDC said those most at risk for RSV include premature infants; very young infants, especially those 6 months and younger; and children younger than 2 years old with chronic lung disease or congenital heart disease. 

Adults and older children who are healthy tend to have mild cases if infected. Early symptoms tend to include a runny nose, a decrease in appetite, and cough. Those symptoms can worsen, causing inflammation of the small airways in the lung.

The vaccine is recommended for all infants younger than 8 months born during or entering their first RSV season, if their mother did not get a maternal RSV vaccine. Another option is for pregnant people to get vaccinated during weeks 32 through 36 of their pregnancy if that period falls between September and January.