The seasonal timing of when infants receive the new respiratory syncytial virus (RSV) immunization is crucial for ensuring its effectiveness, according to Yale research published in .
Nirsevimab is a seasonal immunization that targets RSV in infants. As a monoclonal antibody鈥攁 protein that can bind to a specific target鈥攏irsevimab binds to a particular area of the virus and blocks RSV from entering human cells.
In a new study testing the effectiveness of the monoclonal antibody in a real-world setting, researchers at Yale School of Medicine (YSM) found that immunization was up to 85% effective at preventing serious illness in children under one year of age. However, timing its administration to coincide with seasonal outbreaks is important because the monoclonal antibody鈥檚 effectiveness waned three months after receiving the shot.
Children with severe RSV 鈥渁re essentially drowning in their own mucus,鈥� says , assistant professor of pediatrics (infectious diseases) at YSM and senior author of the study. So having immunizations that can prevent this and keep vulnerable infants from ending up in the hospital 鈥渋s huge,鈥� he says.
A dangerous disease
RSV is incredibly common. Almost every child will contract the virus before the age of two. Some people who get RSV only develop a runny nose and fever. But for infants and elderly patients, the virus can be deadly.
鈥淎ny parents of a baby with severe RSV will see how their child is constantly struggling to breathe,鈥� says Oliveira, who is also an assistant professor of biostatistics at Yale School of Public Health. Excessive mucus produced to fight off the virus can clog the small airways of children under the age of six months. Globally, around 1.4 million children under the age of six months end up hospitalized due to RSV every year, mostly during the fall and winter. Of those, approximately 27,000 will die.
There is no targeted treatment for RSV. But in July 2023, the U.S. Food and Drug Administration (FDA) licensed nirsevimab as the first single-dose, long-acting monoclonal antibody for the prevention of RSV in infants. Previously, palivizumab was the only preventative option and required monthly injections to sustain its protective effect.
Clinical trials found nirsevimab to be safe and effective for infants. This study is an important continuation of that research. Vaccines and medications are still studied after FDA approval to track their effectiveness in the general population鈥攐utside of the clinical trial setting鈥攁nd further inform optimal use. These types of studies are considered phase IV trials.
RSV immunization prevents severe illness
Oliveira and his colleagues collected data on approximately 3,000 infants who received care in the Yale New Haven Health System for respiratory illnesses between October 2023 and May 2024. This was the first RSV season in which nirsevimab was available, and only 10% of infants in the study had received the immunization before seeking medical help.
Of the 3,000 infants, the researchers tracked who had tested positive for RSV, who had been immunized, and how they fared across the study period. About 680 infants tested positive for RSV, and 166 infants鈥�97% of whom had not been vaccinated with nirsevimab鈥攅nded up hospitalized.
The data showed that the monoclonal antibody didn鈥檛 provide total protection against RSV; nirsevimab was around 68% effective at preventing RSV infection in infants. However, the researchers found that immunization was 85% effective at preventing infants from being hospitalized.
So, while nirsevimab didn鈥檛 prevent all RSV infections, 鈥渢he key takeaway is that the monoclonal antibody was very good at preventing severe disease,鈥� says Oliveira. Immunization was the difference between an infant with a runny nose and one that ended up in the ICU.
Oliveira and his colleagues鈥� research also shows that nirsevimab becomes less effective after about 14 weeks. The U.S. Centers for Disease Control and Prevention recommends that infants who are eight months old or younger receive the shot at the very start of the RSV season, which runs between October and March.
Information from Oliveira鈥檚 study will help policymakers decide when to roll out nirsevimab during the RSV season.
The research reported in this news article was supported by the National Institutes of Health (awards R01AI179874 and K23AI159518) and by Yale University. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
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