New Drug to Help Prevent RSV in Babies is Effective in Preventing Hospitalization, Study Says

This is the first RSV season the medication has been available for infants.

Medically reviewed by Monika Goyal, M.D.Fact checked by Sarah Scott

Most parents know about those three dreaded letters. The ones that come after days of misery for your child: the fever, the cough, the runny nose, and trouble breathing. That’s right, RSV, or respiratory syncytial virus.

In late July 2023 came hope for parents. The Food and Drug Administration (FDA) approved a new medication that can help prevent the virus in babies and toddlers. It's called nirsevimab (brand name Beyfortus) and is made by AstraZeneca. It can be given to newborns and babies born during or entering their first RSV season—and to toddlers up to 24 months who are going into their second RSV season.

“Many parents have had an experience with RSV in their lives that hasn't been great,” says Gigi Chawla, MD, MHA, chief of general pediatrics at Children’s Minnesota. “I think the utility of this type of treatment will be seen by parents differently than perhaps other vaccine offerings we've had”

The American Academy of Pediatrics (AAP) quickly followed the FDA approval with a recommendation of its own: that all infants should receive the treatment to protect them against severe RSV. The organization is recommending a single dose of the medication for all infants younger than 8 months born during or entering their first RSV season as well as babies and toddlers between 8 and 19 months who are at high risk.

The Centers for Disease Control and Prevention (CDC) also recommends the shot, with the same guidelines as the AAP.

This is all for good reason. In a CDC study released on March 7, 2024, nirsevimab was 90% effective in preventing hospitalization associated with RSV in babies. Researchers studied 699 infants between October 2023 and February 2024. The CDC does caution these results are from a shorter period of time because the drug was not introduced until August of 2023. The CDC says it will continue to evaluate its effectiveness over time, especially as the drug becomes more widely available.

Unprecedented Demand for RSV Treatment

Despite these recommendations, this RSV season the treatment has been hard to come by due to a short supply. The drugmaker says they've seen unprecedented demand for the medication.

Therefore, the CDC is asking health care providers to ration nirsevimab during the 2023-2024 RSV season.

"Despite an aggressive supply plan built to outperform past pediatric vaccine launches, demand for this product, especially for the 100 mg doses used primarily for babies born before the RSV season, has been higher than anticipated," Sanofi says in a press release.

Due to this demand, the CDC is recommending health care providers prioritize nirsevimab 100 mg doses for the babies most at risk for severe RSV. Those are infants under 6 months and those with underlying conditions. The CDC isn't recommending a change for 50 mg doses—but caution providers to avoid using two 50 mg doses for infants under 11 pounds to help preserve the supply.

Boost in Supply

On November 16, 2023, the CDC says it has released more than 77,000 additional doses of nirsevimab. They are distributing the doses to doctors and hospitals through the Vaccines for Children Program and commercially. While this does temporarily alleviate the shortage, they are still recommending the doses be given to those at highest risk. The CDC and the Food and Drug Administration (FDA) are working with manufacturers to source additional doses.

Equitable Access

The CDC's Advisory Committee on Immunization Practices (ACIP) also voted to include nirsevimab in the Vaccines for Children program. This program provides vaccines at no cost to children in need.

The AAP is also calling for a national strategy to make sure there is equitable access to nirsevimab in all health care settings. The president of the AAP, Sandy Chung, MD, FAAP sent a letter to the director of the Centers for Disease Control and Prevention (CDC) along with the administrator of the Centers for Medicare and Medicaid Services (CMS) urging them to improve the infrastructure for delivering the medication.

“Pediatricians are sadly familiar with the dangers of RSV and its devastating consequences for some families,” Dr. Chung says in a news release. “We are eager to offer all infants this protection and urge federal officials to see that it is made available and affordable in all communities.”

RSV can affect people of all ages, but children under 5 are at more risk of complications and can be more susceptible to contracting it. While RSV will likely pass through preschoolers like a bad cold, it can be a bit more worrisome in kids under the age of 2 who may experience it more as a lower respiratory tract infection like bronchitis or pneumonia.

An Increase in RSV Cases

Cases of RSV have risen significantly over the past two years, due in part to the pandemic. Most instances of the viruses used to happen in the fall and winter months, but, as Marc D. Foca, MD, Division of Infectious Diseases at Children's Hospital at Montefiore explains, there’s been an increase in RSV cases in the summer as well.

“Early in the pandemic, cases of all respiratory viruses plummeted, probably because of masking, social distancing, and frequent hand sanitizing,” Dr. Foca says. “For infants and children, the first episode of RSV is often the most severe, so when practices loosened, a large cohort (many millions) of young children were exposed to their first RSV infection and other common viral infections at the same time."

That sudden exposure is probably one of the reasons RSV infections have gone up, but it’s hard to tell whether this trend will continue or if the case numbers will return to pre-COVID levels, Dr. Foca adds. That surge in cases is being felt by hospitals and across the country.

“We had a very challenging RSV season last season, something that I think was very much unprecedented, unpredictable, and certainly taxed the entire healthcare system just with how many cases of RSV there were and the severity of it,” Dr. Chawla recalls.

Related: 7 Common Baby and Toddler Illnesses and How to Treat Them

A New Tool to Prevent RSV

While there have been some preventative measures against RSV (including good, old-fashioned hand washing) for children before the FDA’s approval of Beyfortus, they’ve largely been reserved for those who are at higher risk and would be administered over a five-month period.

“Nirsevimab is a breakthrough as only one injection is needed to cover a child for the entire RSV season,” Dr. Foca says. “This medicine binds better to the target protein on RSV than the previous prevention method—and it is approved for all infants in their first RSV season (regardless of their risk profile; they can be preterm).”

The injection itself is pretty remarkable in how it functions. Unlike traditional vaccines, like the flu shot, or newer methods, like the RNA COVID-19 shot, the recently-approved RSV injection is not a vaccine at all, but rather an antibody delivered through intravenous means, giving your body the treatment for RSV it needs so it doesn’t have to work to create it.

“This is an antibody,” Dr. Chawla explains. "So what you're doing is you're already giving your body essentially the antidote so that it doesn't have to create the antidote. That means that it's going to work for a season, and then it's gone.”

The medication went through three clinical trials before being approved. The trials showed the treatment to be safe and effective in protecting healthy late preterm and term infants from severe RSV.

"This is an antibody. So what you're doing is you're already giving your body essentially the antidote so that it doesn't have to create the antidote. That means that it's going to work for a season, and then it's gone."

Gigi Chawla, MD, MHA

Concerns With the New RSV Medication

As with any drug, Beyfortus comes with possible side effects which include rash and injection site reactions, according to the FDA. It should also not be given to infants and children with a history of serious reactions to the drug’s active ingredients.

It’s also important to note that parents shouldn't worry if their child still gets sick even after they are given the drug. The antibody administered does not completely block all infections, but that does not mean it’s not working.

“During the medical trials, the focus was on lowering the number of infants who needed care in a physician's office, an emergency department, or a hospital,” Dr. Foca explains.

The Future of RSV Prevention

Though it’s still not clear when the drug will be commercially available, its approval is a major step toward significant prevention measures. But aside from the drug being a breakthrough for RSV, it also sheds new light on the possibilities for preventative measures for other types of viruses as well.

“I think right now, we're all still learning so much, we're right there with you where we're hearing about this vaccine or drug, just as it's come to market with the FDA approval,” says Dr. Chawla. "But I think it's got great potential.”

Another tool in the pipeline is an RSV vaccine given to pregnant people. The vaccine would transfer protection to their babies. According to Pfizer's research, the vaccine was 82% effective in preventing hospitalization in infants younger than 90 days. It also offered protection up to 6 months old. Pfizer could see FDA approval by the end of the summer.

Related: What Is Coxsackievirus?

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