FDA approves Pfizer’s RSV vaccine for pregnant women

A first-of-its-kind RSV vaccine for pregnant women protects their newborns against the dreaded respiratory virus — and federal health advisers on Thursday backed Pfizer’s shot despite some objections questions.

RSV fills hospitals with crying children every fall and winter, and the virus hit earlier than usual and especially hard in the US this past year.

If the vaccine goes away, “many babies and their parents will breathe easier for years to come,” said Dr. Jay Portnoy, a member of the Food and Drug Administration advisory panel from Children’s Mercy Hospital in Kansas City, Missouri.

The idea: Give women an injection late in pregnancy, between 24 weeks and 36 weeks, so they can produce RSV-fighting antibodies that pass through the placenta – just as they pass on protection against other bugs to their children.

At Pfizer’s international studies in nearly 7,400 pregnant women, maternal vaccination proved to be 82% effective in preventing severe RSV during the children’s most vulnerable period in the first three months of life. At the age of 6 months, it still proved to be 69% protective against severe disease.

Pfizer said there was no indication of safety problems but the FDA asked its scientific advisers to consider whether the small difference in premature births between vaccinated mothers and those given a dummy shot was concerning. Debate whether this was a sign of trouble or just a coincidence that dominated the entire day’s panel meeting.

Pfizer has promised to closely monitor real-world use of the vaccine for more evidence. In the end the advisers unanimously decided that the shot was effective – and voted 10-4 that there was enough safety data. The FDA will consider the recommendations on Thursday when making a final approval decision.

“If you are at risk of premature birth with this vaccine, I think there is a high price to pay,” said Dr. Paul Offit of the Children’s Hospital of Philadelphia, among the panelists who voted “no” on safety. question

If the FDA finally approves the maternal shot, it will mark the second milestone in the decades-long quest to prevent respiratory syncytial virus. Earlier this month it was approved by the FDA the world’s first RSV vaccine, GSK’s rival shot for the elderly, which also carries risks. There is no vaccine for children yet, but Pfizer is about to start testing one.

Here are some things to know:

RSV is a common threat

For most healthy people, RSV is a cold-like nuisance. But it can be life-threatening for very young children — infecting the deep lungs causing pneumonia or interfering with children’s breathing by swelling their small airways. In the US alone, between 58,000 and 80,000 children younger than 5 are hospitalized each year, and between 100 and 300 die, according to the Centers for Disease Control and Prevention.

“All infants are at risk of serious illness with RSV,” but delaying infection even for a few months can reduce that risk, said Dr. Katherine Fleming-Dutra of the CDC.

The potential side effects of the vaccine

The Pfizer vaccine is not intended to prevent RSV infection but to prevent its worst consequences. In a late-stage trial, six infants born to vaccinated mothers had severe RSV disease in their first three months of life compared with 33 infants whose mothers received a dummy shot. In addition, the vaccine cuts in half the chances of needing any medical attention for RSV infection by age 6 months.

The company predicts that the US could prevent up to 20,000 childhood hospitalizations a year, and 320,000 doctor visits, if enough pregnant women were vaccinated.

Safety data

Vaccine reactions include usually mild pain at the injection site and fatigue. As for the prematurity question, vaccinated mothers had slightly more preterm babies — 5.7% versus 4.7%. Most are born just a few weeks early. That’s better than the nation’s preterm birth rate — in the U.S. as a whole, 1 in 10 babies were born prematurely last year — and the imbalance in the study was not statistically significant, meaning it was due by chance.

Competitor GSK halted its own trial of a maternal RSV vaccine due to premature concerns, prompting questions about Pfizer’s shot. Pfizer said the preterm difference in its study was driven by South African participants — for unknown reasons — and no difference was seen in the US or other high-income countries.

“Are you holding the potential benefits of the vaccine hostage” without clear evidence of a problem, Dr. William Gruber, the senior vice president of Pfizer, the panelists.

“There is certainty that the vaccine will work and keep babies out of the hospital in the United States this winter,” he said.

In total, 17 infants died during the study, five born to vaccinated mothers and 12 to those given a dummy shot. The researchers considered none of the deaths to be related to the vaccine but the FDA said it “cannot exclude the possibility” that the death of an infant, which resulted from severe prematurity, could be related.

Vaccines have always come under strict safety scrutiny, but regulators were particularly concerned about a major failure in the 1960s when an experimental RSV shot worsened infections in children. Scientists eventually caught on to the problem and the RSV vaccines in the pipeline are now being made using safer, modern methods – though tested on older people first.

Another open question

FDA advisors also cautioned that it is not clear which other vaccines given to pregnant women may be administered during the same doctor’s visit. They pointed to data suggesting that a vaccine against whooping cough may not be as effective if pregnant women receive it at the same time as the RSV shot.

What happens next?

FDA advisors have already recommended approval of Pfizer’s vaccine for the elderly, and the agency is expected to make a decision by the end of the month. Whether to use the same shot in pregnant women will be a different decision by the FDA, expected in August.

Meanwhile, rival GSK is preparing for fall vaccinations with an RSV vaccine for the elderly. First, CDC advisers will debate next month whether all seniors or those at high risk should be vaccinated.

Vaccines are not the only development in the pipeline. High-risk infants can get a monthly dose of a protective drug during RSV, although CDC data shows that few receive it. European regulators recently approved the first single-dose option, from Sanofi and AstraZeneca, opening that type of protection to more babies. FDA advisers will also debate that drug next month.


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. AP is solely responsible for all content.

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