How new RSV antibodies help protect infants worldwide

Every year, a virus called RSV (respiratory syncytial virus) puts millions of babies and young children in the hospital. Although RSV often acts like a really nasty cold, it can be dangerous for newborns, especially those born early or with weak immune systems. But thanks to smart scientists and doctors, new ways to protect infants from RSV are on the horizon, making it easier and safer for more babies across the world to stay healthy (Nature Biotechnology, 2025).

What is RSV and why is it a problem for babies?

RSV is a tricky virus that mostly causes cold-like symptoms in healthy people, but for infants and older adults, it can be much more serious. Each year in the United States, RSV leads to about 58,000 hospital stays for children under age five. Worldwide, the numbers are even more worrying, with nearly 3 million hospitalizations and up to 100,000 deaths in children under five, mostly in countries where healthcare resources are limited (The Lancet).

Old and new ways to fight RSV

For a long time, there was only one medicine to protect at-risk babies from RSV: an antibody shot called Synagis, which has been around since 1998. Synagis helps, but it only reduces the risk of RSV hospital visits by about half. A newer antibody, Beyfortus, was approved in 2023 and works even better, thanks to clever science that helps it last longer and protect more babies with just one shot instead of five. Beyfortus targets a special part of the RSV virus, making it harder for the virus to sneak past our defenses (BMC Infectious Diseases).

Now, Merck has developed a new antibody called clesrovimab, which could be approved very soon. This shot is especially exciting because it targets a different part of the virus, giving doctors another tool if the virus ever changes and becomes resistant to older medicines. In big studies, just one dose of clesrovimab helped prevent more than 90% of RSV hospitalizations in preterm babies, and it was as effective as five doses of Synagis in preventing serious illness. Plus, clesrovimab is given as a fixed dose, so it's simple for doctors to use.

The challenge of making vaccines for babies

Vaccines are another powerful way to stop RSV, but making safe and effective RSV vaccines for babies has been tough. In the past, some vaccines made the illness worse instead of better, especially for the youngest children, because their immune systems work differently than adults' (The Journal of Pediatrics). Scientists have learned a lot since then, and now there are vaccines for older adults and pregnant women. When expectant mothers get vaccinated, they pass protective antibodies to their babies before birth. Pfizer's Abrysvo is one such vaccine, and it has already helped protect many newborns around the world.

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Access and affordability: getting protection to every baby

A big challenge is making sure all babies—no matter where they live—can get these life-saving medicines. Antibody shots are expensive to make, and even with price cuts, they can cost $5–10 per dose. Vaccines, especially those given to pregnant mothers, can be more affordable, but only if countries have the right programs in place. Some countries, like Argentina, are using the maternal vaccine, while others, like Chile, are giving antibody shots to all newborns. Experts hope that as more treatments are approved, prices will drop, and more babies will be protected.

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The future: more options and better protection

The World Health Organization now recommends that all countries use both maternal vaccines and antibody shots to protect babies. More research is happening, including work on live vaccines that could protect children as they get older. Scientists are also learning from these new RSV treatments to develop antibodies that might one day protect against other tough viruses like HIV (Immunity).

With the help of health AI, platforms like SlothMD are bringing the latest information and research to doctors and families, making it easier for everyone to keep up with new ways to stay healthy. As more options become available and prices come down, the hope is that every baby, everywhere, can get the protection they need from RSV.