The Food and Drug Administration on Monday approved a vaccine to prevent respiratory syncytial virus infections in infants during their first few months of life, giving an OK to Pfizer’s shot Abrysvo for use during pregnancy.
The vaccine, which the agency cleared earlier this year for older adults, can pass on protection from the virus to newborns, whose budding immune systems leave them at higher risk of infection. Regulators in Europe last month similarly recommended Abrysvo for use during pregnancy.
“This approval provides an option for healthcare providers and pregnant individuals to protect infants from this potentially life-threatening disease,” said Peter Marks, head of the FDA office that reviews vaccines, in a statement.
Respiratory syncytial virus, or RSV, is very common and typically causes cold-like symptoms. But it can be more serious in some, causing lower respiratory tract disease that leads to the hospitalization of tens of thousands of young children each year.
It can also be dangerous for adults over the age of 60, a group for which Abrysvo won FDA approval in May, joining GSK’s first-of-its-kind RSV vaccine on the market.
While there are antibody treatments available for young babies, including one endorsed by the FDA in July, Abrysvo is the only vaccine available as a maternal immunization.
“There’s a lot going on in the mom's life and the baby's life after birth, and so the ability to just have protection gifted from birth, that's just really, really magical,” said Iona Munjal, executive director of Pfizer’s vaccine clinical research and development, said in an interview ahead of the FDA’s decision.
Drugmakers have spent decades trying and failing to develop a safe and effective vaccine for RSV. The recent flurry of approvals for GSK and Pfizer is the product of a scientific breakthrough that helped researchers design better shots. Large clinical trials have now proved their worth in both older adults and pregnant people.
For maternal use, Pfizer tested Abrysvo in an international trial of pregnant women between 24 and 36 weeks gestation, who received either a dose of Abrysvo or placebo. Their babies were then followed after birth to compare rates of lower respiratory tract illness.
Results, which were published in The New England Journal of Medicine showed that vaccination protected infants from medically attended severe RSV-associated lower respiratory tract illness within 90 and 180 days of birth. However, the study missed its goal of also proving the vaccine provided equally strong protection against milder disease.
The most common side effects reported in testing were injection site pain, headache and nausea in pregnant people who received the shot. A potentially dangerous hypertensive disorder called pre-eclampsia occured in a 1.8% of vaccinated participants, compared to 1.4% of those given placebo.
FDA advisers, discussing the shot at a May meeting, also noted an apparent increase in premature births in lower-income countries. However, the study was not set up to properly assess that risk and advisers ultimately voted in favor of the shot’s effectiveness and safety.
The FDA’s approval is limited to only between 32 and 36 weeks gestation, a narrower window than Pfizer had studied. In its statement, the regulator said that, while the available data don’t establish a causal relationship between preterm birth and the shot, doctors should avoid vaccinating pregnant individuals before 32 weeks gestation.
The FDA is requiring Pfizer do follow-up testing to further assess the potential risk of preterm birth and other reported side effects like pre-eclampsia.
GSK had also been developing a maternal RSV vaccine but halted its trial last year after detecting a safety signal. The company hasn’t fully detailed the study’s results.
With an FDA approval now in, an advisory panel to the Centers for Disease Control and Prevention will meet to develop recommendations for the vaccine’s use.
Abrysvo will give expecting parents in the U.S. another option for protecting their child alongside a newly approved monoclonal antibody from partners Sanofi and AstraZeneca. Called Beyfortus, the antibody acts as a passive immunization to protect infants up to two years old.
Researchers and regulators are currently weighing whether the drug can be safely given to a newborn whose mother was vaccinated with Abrysvo, and whether that will add any additional protection.