Medical Minute: FDA Approves First RSV Vaccine For Pregnancy To Protect Newborns

Expectant parents could soon have another new option this fall to protect their newborns from RSV, or respiratory syncytial virus, the most common cause of hospitalization in American infants, after the Food and Drug Administration announced Monday that it has widened its approval for Pfizer's Abrysvo vaccine to include expectant mothers. 

Pregnant women would receive immunity from the shot during pregnancy then pass that along to their baby before birth, offering protection in the infant's earliest months of life. 

"This approval provides an option for healthcare providers and pregnant individuals to protect infants from this potentially life-threatening disease," said Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, in a release announcing the approval.

Pfizer's new approval follows a favorable vote from the FDA's outside vaccine advisers in May, after results finding the shot had 69.4% efficacy in lowering the risk of severe lower respiratory tract illness in babies through six months after birth. 

If the Centers for Disease Control and Prevention concurs, the shot would be added to a list of "maternal vaccines" recommended before birth, buoying the chances of newborns making it safely through some of their most vulnerable months of life. 

"Today, a long-sought-after goal to deliver a maternal vaccine that will help protect infants six months of age or younger – when they are at greatest risk of possible serious consequences from RSV – has been achieved," Annaliesa Anderson, Pfizer's chief scientific officer of vaccine research and development, said in a statement. 

While nearly all children will have survived at least one RSV infection by age 2, the virus can be especially dangerous to babies who contract their first bout of the disease in their youngest months.

The FDA had previously approved Pfizer's Abrysvo vaccine only for use in older adults. Adults ages 60 and older are recommended to talk to their doctors about potentially getting the shot.

The CDC's Advisory Committee on Immunization Practices will need to meet again to weigh updated recommendations for the shots during pregnancy. 

While doctors are not bound by law to follow the panel's recommendations, they do play a key role deciding requirements for insurance coverage of the vaccines. 

A second option for protecting newborns

The latest approval follows another option that was recently greenlighted to protect babies from RSV: nirsevimab, an antibody injection which is now being marketed as Beyfortus by drugmakers Sanofi and AstraZeneca. 

After a meeting in early August, the CDC had signed off on new recommendations urging parents of babies born into their first RSV season this fall and winter to get them the Beyfortus shot.

But agency officials acknowledged the committee would need to meet again to vote on new recommendations if Abrysvo was also approved by the FDA, sorting out how it might affect their new guidance.

Both Abrysvo and Beyfortus appeared to be safe and effective in trials at curbing RSV hospitalizations in babies, a work group convened by the agency reported earlier this year. 

However, preliminary calculations presented to the committee suggest it would not be cost effective to issue recommendations for giving both shots, which together were modeled to cost $700 for each child before insurance. 

Instead, the CDC may end up favoring recommendations to offer Abrysvo first. 

Beyfortus would effectively be a backup, under their draft guidance, largely offered only to babies born to parents who did not get Abyrsvo during pregnancy or who are at higher risk of severe disease.

Questions about very rare preterm births

Further complicating the new recommendations are a handful of very rare preterm births seen in babies of moms who received Abrysvo during pregnancy. 

While the number in Pfizer's trial was too small to be statistically significant, it came after a larger uptick in preterm births was big enough to force GSK to halt a separate RSV vaccine trial in pregnant women earlier this year. 

"We have had long discussions about whether or not there could, or is not, a biologic plausibility to this," the CDC's Katherine Fleming Dutra told the ACIP at a meeting in June.

This puzzled some on the FDA's vaccines panel earlier this year as well. While they voted unanimously in favor of its effectiveness, the panel split 10 to 4 voting in favor of whether there was enough data on Abrysvo's safety to back its approval. 

"I'm troubled, as everybody is, by the prematurity issue. And I'm not sure that running it through another maybe season is going to give us an answer. And I think we've heard that observational studies, as we go forward, will fairly quickly give us an answer if there is a problem there," Dr. Arnold Monto, one of the FDA committee's members, said at the meeting.

The FDA said Monday it would require Pfizer "to conduct postmarketing studies" to assess the risk of preterm birth, and will include a warning about the "numerical imbalance."

"The available data are insufficient to establish or exclude a causal relationship between preterm birth and Abrysvo," the agency said.

The shot is also only approved to be given towards the end of the third trimester, later than the 24 weeks minimum that was set in Pfizer's trials.

"Part of the reason these are being given so late in pregnancy, 32 to 36 weeks of pregnancy, so the third trimester, is really to minimize any risk to the baby," Dr. Celine Gounder, a CBS News medical contributor and editor-at-large for public health at KFF Health News, told "CBS Mornings" on Tuesday.

"The idea is to vaccinate early enough that you provide the protection to the baby, but late enough that there aren't significant risks associated," Gounder said.