New Monoclonal Antibody and Vaccine Can Protect Kids from RSV > News > Yale Medicine

BY KATHY KATELLA August 28, 2023

[Originally published: August 14, 2023. Updated: August 28, 2023]

Last fall and winter were worrisome for many parents as children’s hospitals across the country filled to capacity with infants and toddlers infected with respiratory syncytial virus (RSV). The virus causes a runny nose and other cold-like symptoms in older children and most adults, but it can lead to severe illness in the youngest and oldest patients. A dip in cases during the COVID-19 pandemic led to lower immunity to RSV, and the disease came roaring back last year.

The upcoming RSV season could be much easier, thanks to the Food and Drug Administration (FDA)’s approval in July of nirsevimab (brand name: Beyfortus™), a monoclonal antibody. In August, the Centers for Disease Control and Prevention (CDC) signed off on the drug for all infants up to 8 months old, born during—or entering—their first RSV season, and for a small group during their second season if they are between 8 and 19 months old and at high risk for severe disease (including children who are severely immunocompromised).

In August, the FDA approved another new preventive tool. Abrysvo™ is the first vaccine to be given to pregnant individuals so they can pass along protection to the fetus and prevent severe RSV disease in newborn infants. The vaccine is awaiting a final recommendation by the CDC, and it’s unclear whether it will be available for the coming RSV season.

“This is extremely exciting for both parents and pediatricians,” says Thomas Murray, MD, PhD. “Nirsevimab should reduce hospitalizations. Even if it doesn't completely prevent infection, we expect it will reduce disease severity significantly.”

The nirsevimab approval came a month after the CDC finalized two new RSV vaccines for adults ages 60 and older. Those vaccines are expected to be available by early fall as well, heading off a spike in seasonal hospitalizations for older adults, another group at increased risk for the virus.

It’s important to note that nirsevimab for children works differently than the RSV vaccines for adults (more on that below). Dr. Murray answered questions about the new preventive option for children.

Nirsevimab is a monoclonal antibody (designed by pharmaceutical companies Sanofi and AstraZeneca), which was given an FDA Fast Track designation, a process designed to expedite drugs to treat serious conditions and fill unmet medical needs. It’s a preventive option that mimics the immune system’s ability to fight off invaders, such as viruses, providing an extra layer of defense against RSV, according to the CDC. (It is not intended to treat patients already sick with the virus.)

As a monoclonal antibody, nirsevimab approaches prevention differently than a vaccine would. “A vaccine causes your body to produce antibodies to protect you against whatever virus the vaccine is targeting,” Dr. Murray says. “The monoclonal antibody bypasses that step.” Once introduced into the body, nirsevimab functions as a form of passive immunity that is ready to bind to the RSV virus and block it from infecting healthy cells, preventing severe disease.

RSV is a highly contagious virus that spreads rapidly among children. The virus can live for hours on surfaces, such as doorknobs, countertops, and crib rails, and then spread when people touch their face after touching those surfaces. It also spreads through the air, often when a person infected with the virus coughs or sneezes, and droplets get in another person’s eyes, nose, or mouth. So, it's important to avoid close contact with an infected person.

The infection can make its way down into the lungs, causing a clinical syndrome called bronchiolitis (inflammation of the small airways in the lungs) that results in difficulty breathing; it’s especially risky for those born prematurely or with underlying medical conditions, such as congenital heart disease.

In children younger than age 5, there are approximately 2.1 million RSV-related outpatient visits a year in the U.S. Many babies won’t need to go to the hospital, but in a given year, 58,000 to 80,000 of them do, and there are 100 to 300 deaths.

“Young babies are nose-breathers, so if their nose gets clogged, that can contribute to respiratory problems,” Dr. Murray says, adding that RSV is also the most common cause of pneumonia. “They can develop life-threatening complications. Plus, early infection with RSV is a risk factor for developing asthma later in childhood.”

There is no treatment for RSV beyond hydration, over-the-counter medicines to control fever, if present, and close monitoring for difficulty breathing. Severely ill babies may need to go to the hospital for intravenous fluids, supplemental oxygen therapy, and, in rare cases, mechanical ventilation (a machine to help them breathe).

Nirsevimab is given by intramuscular injection into the thigh muscle. A single dose may cover an entire RSV season, which starts in the fall, peaks in the winter in most parts of the U.S., and can last through spring. (The cycle was disrupted during the COVID-19 pandemic, and experts hope to see it return to normal this fall.)

Sanofi and AstraZeneca tested the shot in 3,200 infants in studies before submitting data to the FDA. One study, published in the New England Journal of Medicine, found nirsevimab to be 79% effective against RSV severe enough to warrant medical attention. A panel of independent advisors to the FDA voted unanimously to recommend approving the preventive option.

Common side effects are reactions, such as rashes or visible irritation, at the injection site. Nirsevimab comes with warnings about anaphylaxis (a life-threatening allergic reaction), and it should be given with caution to infants and children with clinically significant bleeding disorders, according to the FDA.

Older children aren’t at high risk for severe disease from RSV. Almost all children older than age 2 have had the virus already and have some immunity to protect them, Dr. Murray explains. By the time they are teenagers, they usually have strong immunity from multiple exposures and experience RSV as a mild cold. Rarely, they develop respiratory complications or severe disease.

Immunity from RSV continues well into adulthood. However, older adults start to lose immunity as they age—they're unable to fight off infections, such as RSV, as well as they did when they were younger. “That's why there are vaccines for people over 60,” Dr. Murray says.

Abrysvo, the vaccine by Pfizer that was FDA-approved in May to prevent RSV in people ages 60 and older , was recently approved for pregnant women at 32 through 36 weeks of gestational age. Abrysvo, which is given by injection into the muscle, helps pregnant women develop antibodies against RSV that they would pass along to the fetus—and when their baby is born, he or she would be protected for the first six months of life.

In a study published in the New England Journal of Medicine, the vaccine showed 81.8% efficacy in preventing severe respiratory illness within three months after birth and 69.4% in the first six months of life in clinical trials.

When an independent advisory committee to the FDA voted in May to recommend approval of the shot, a few independent advisors expressed concern about a slight increase in preterm births among women who were given the vaccine—5.6% in vaccinated women compared to 4.7% in an unvaccinated group. While the 14-person panel recommended the Pfizer shot unanimously based on its efficacy, it voted 10-4 based on whether the data supported its safety. But, according to the FDA, the available data was insufficient to establish or exclude a causal relationship between preterm birth and Abrysvo. The agency is requiring Pfizer to conduct post-marketing studies to assess the signal of serious risk of preterm birth.

Parents should help children at high risk for severe RSV take precautions, including avoiding close contact with sick people. “Parents also can teach children to wash their hands with soap and water for 20 seconds to help ensure they are not touching their faces with dirty hands after touching shared toys and other potentially contaminated surfaces,” says Dr. Murray.

Parents also can talk to their pediatrician about whether the new monoclonal antibody is appropriate for their child and follow news about the potential vaccine, Dr. Murray adds.

“Any therapy that we can give safely and that will reduce hospitalization for babies is helpful to everybody,” Dr. Murray says, adding that fewer RSV-related emergency room visits will benefit everyone, from the infants themselves to older children and adults seeking urgent care for other ailments, who will then be able to receive prompt care in hospitals that aren’t overwhelmed.