RSV and RSV Vaccines

Each year, respiratory syncytial virus (RSV) hospitalizes between 58,000 and 80,000 children under 5 in the United States. In the global community, RSV is the second leading cause of death for children under one after malaria. Recently, however, pediatricians are seeing progress against the virus on two fronts: monoclonal antibody against RSV and a maternal RSV vaccine.  

An atypical RSV season 

Before 2020, peak RSV season consistently fell between fall and spring in temperate climates. The COVID-19 pandemic interrupted this cycle. Healthcare professionals noted a rise in RSV in spring of 2021, with a peak later that July. 2022 saw a continuation of unusual trends, with a surge in hospitalizations in November and December contributing to the “tripledemic” and fueling research efforts into effective prevention. 

Related: Pediatric Pharmacology: Immunizations


A monoclonal antibody against RSV, palivizumab, has been on the market since 1998. Made by AstraZeneca, palivizumab has limited potency and degrades relatively quickly, meaning infants must receive five monthly shots — which, all told, cost several thousands of dollars — to ward off the disease.  

It’s one reason why the antibody is only given to babies at highest risk of developing severe disease from RSV, such as those born prematurely with underlying heart or lung diseases. In the United States, about 2% of babies receive palivizumab prophylactically. 

Dr. Cody Meissner, an RSV researcher at Tufts University, says there’s “no question” that palivizumab works. He notes, however, that more than 80% of infants who develop severe RSV disease are full-term, healthy babies at birth. Developing an RSV monoclonal that is safe, effective, and easy to administer to a wider population is the real goal.  

So far, monoclonals that sought to improve on palivizumab’s modest success have failed to win regulatory approval. 

Promising test results 

Nirsevimab, a new monoclonal developed by AstraZeneca in collaboration with Sanofi Pasteur, may fit the bill. It has a higher potency and more than three times the half-life of palivizumab, meaning a single shot can last for an entire season.  

In a trial among 1,500 preterm infants in 23 countries, researchers have shown that babies who received a single shot of nirsevimab within 2 months of the start of the season were 78.4% less likely to end up in the hospital with RSV-associated lower respiratory disease than those who received a placebo. 

“They’re beautiful results,” says Barney Graham, a researcher at the U.S. National Institute of Allergy and Infectious Diseases, who was not involved with the study. Meissner agrees that nirsevimab “looks like a pretty interesting product.” 


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