As the number of RSV cases grows, the CDC warns of a shortage of a key drug to ensure children's safety.

The Centers for Disease Control and Prevention (CDC) warned doctors across the country on Monday about the limited availability of certain doses of a recently approved antibody-based drug prescribed to infants to prevent RSV infection as the cold and flu season begins.

With the start of the cold and flu season, the number of RSV (respiratory syncytial virus) cases has started to rise.

"The RSV season is here," said Dr. Buddy Creech, a pediatric infectious disease physician at Vanderbilt University Medical Center in Nashville, Tennessee. "We're seeing a significant uptick in RSV cases, so in many regions, it has become the most commonly identified respiratory virus causing illness in children."

"This is one of the reasons why there is likely a lot of work being done to identify those children at the greatest risk and try to prioritize them because right now this resource is so limited," he added.

In July, the Food and Drug Administration (FDA) approved an antibody-based drug called Beaufortus. It is not a vaccine, but it works similarly to a vaccine by delivering antibodies directly into the bloodstream through an injection, rather than prompting the immune system to produce its own antibodies against RSV.

Newborns and infants can receive doses of Beaufortus during the first RSV seasons, and children under 2 years of age who are at high risk of severe illness caused by the virus can receive second doses during the second RSV seasons.

According to the CDC warning, the highest dosage, 100 milligrams, is in limited supply. The agency advised doctors to prioritize obtaining these doses for infants at the highest risk of severe RSV, including infants under 6 months of age and infants with underlying conditions. The CDC also advised doctors to reserve 50 mg doses for infants weighing less than 11 pounds.

Sanofi, the drug manufacturer, stated in a press release on October 13, "Despite an aggressive supply plan designed to surpass prior launches of pediatric vaccines, demand for this product, especially the 100 mg doses primarily used for infants born before RSV season, has been higher than anticipated."

The FDA has not listed the drug as in shortage in its database.

Another option for preventing RSV infections in infants is the antibody-based drug Synagis. However, it is only approved for infants at high risk and can only be prescribed during the RSV season.

In August, the FDA approved the RSV vaccine Abrivio for use by pregnant women in their third trimester of pregnancy. This provides protection for their children during the first six months of life.