As RSV cases tick up, CDC warns that a key drug to keep babies safe is in short supply

The Centers for Disease Control and Prevention notified doctors across the country Monday of a limited supply of a newly approved anti-viral antibody drug that is given to infants in order to prevent RSV.

RSV (respiratory syncytialvirus) cases are on the rise now that cold and flu seasons has begun.

“RSV season has arrived,” said Dr. Buddy Creech is a pediatric infectious diseases doctor at Vanderbilt University Medical Center, Nashville, Tennessee. “We have seen a significant increase in RSV cases, and in some areas it has now become the leading respiratory virus that causes disease in children.

It’s a very limited resource, so there is a lot more scrambling. “One of the main reasons for this is to identify babies that are at risk.

In July, the Food and Drug Administration (FDA) approved Beyfortus as an antibody drug. It’s not a vaccine but acts like one. Instead of triggering the immune system to produce antibodies to RSV by injection, it delivers antibodies straight to the blood.

Beyfortus is available to infants and newborns who are at risk of serious illness. Children aged 2 and older with a high-risk for the virus may receive two doses.

The CDC has warned that the 100-milligram dose is limited. The agency advised doctors to give the doses first to infants who are at high risk of severe RSV. This includes infants under 6 months old and infants with other conditions. The CDC has also instructed doctors to keep 50 mg doses on hand for infants weighing under 11 pounds.

The drugmaker Sanofi announced in a press release on Oct. 13 that, “despite an aggressive plan to supply this product and outperform other pediatric vaccine launches before, the demand has exceeded expectations, particularly for the 100mg doses used by babies born just prior to RSV season.”

The FDA has confirmed that it does not list the drug as being unavailable in its database.

Synagis is an antibody drug that can be used to prevent RSV in infants. Synagis is approved for only high-risk infants and can be used only during RSV seasons.

The FDA approved Abrysvo, a RSV vaccine for pregnant women during their third trimester in August. This will protect their baby for the first six months.

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This article originally appeared on NBCNews.com