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First RSV vaccine to protect infants wins backing of FDA panel

The first vaccine to protect babies from the respiratory virus RSV is a step closer to approval, after a panel of the Food and Drug Administration's outside vaccine advisers voted Thursday to back the safety and effectiveness of a new shot developed by Pfizer, branded as Abrysvo. 

If ultimately approved by the FDA, Abrysvo could be the first vaccine to protect infants from a respiratory disease that ranks as the leading cause of hospitalization in this youngest age group. Pfizer says the FDA is expected to issue its final decision by August. 

The FDA's Vaccines and Related Biological Products Advisory Committee voted specifically on two questions, weighing whether there was adequate data from clinical trials studying Abrysvo's safety and effectiveness, following a daylong meeting of the panel.

The committee's vote was unanimous favoring data on the efficacy of Abrysvo. The experts voted by a narrower majority, 10 in favor and four against, over whether there was adequate data on the safety of Pfizer's shot.

While the FDA is not required to follow the panel's votes, the agency says input from their outside expert committees will play a key role in its decision.

"These RSV vaccines are based on 21st century science and technology designed to overcome the shortcomings of previous efforts six decades ago," the FDA's Dr. David Kaslow said in opening the meeting.

Attempts in the 1960s to formulate an RSV vaccine given to babies actually appeared to worsen disease from RSV. But a breakthrough by federal scientists in 2013 engineered a new antigen that would pave the way to Abrysvo, as well as laying the groundwork for other new vaccines like the COVID-19 shots.

Pfizer is also looking for the FDA to approve giving their vaccine during pregnancy, instead of directly to babies. That aims to pass on immunity from the expectant mother to their newborn for their first six months of life, when they are most vulnerable, similar to the approach already used for pertussis and flu vaccines also recommended to be given during pregnancy. 

Weighing safety and efficacy

Virtually all children catch their first RSV infection by the time they are 2 years old. Among children under 5, the CDC estimates the virus causes as many as 300 deaths and 80,000 hospitalizations in the U.S. each year.

However, the risk of severe disease is greatest for those who catch it during their earliest months of life. Rates of hospitalization in infants ages 0 to 5 months are more than double those ages 6 to 11 months.

Pfizer's clinical trial results found 69.4% vaccine efficacy in lowering the risk of severe lower respiratory tract illness, through six months after birth. That was well above the minimum criteria to be licensed, the FDA said, though they noted protection against infection is expected to wane as babies age out of their most vulnerable months.

Both FDA and Pfizer concluded that the trial's safety results appeared largely favorable to both pregnant moms and their babies. But the FDA asked their advisers to wrestle with details of a potentially concerning, but too small to be statistically significant, increase in premature births from parents who got the shot compared to placebo.

"I'm troubled, as everybody is, by the prematurity issue. And I'm not sure running it through another, maybe season, is going to give us an answer," said committee member Dr. Arnold Monto.

Pfizer said they planned to continue to study the risk of premature births if the shots are approved, using data from databases of health insurance claims.

Some advisers also echoed concerns raised after rival drugmaker GSK halted its own trials of an RSV vaccine in pregnancy. Pfizer disputed comparisons between their shot and GSK's, underscoring differences in how they are made and the results they got.

"We actually saw just the opposite of that. We've actually seen a lower number of deaths, albeit the total numbers are small, but certainly don't fit with the experience that existed in the other sponsor study," Pfizer's Dr. William Gruber said.

Other RSV immunizations

The Abrysvo shots considered by the FDA advisers Thursday are the same as the Pfizer shot only narrowly backed by this same committee for use in adults 60 and older at a meeting earlier this year

The FDA has not yet made its decision on approval of the vaccine for older adults, which is expected by the end of this month

A vaccine from GSK for Americans ages 60 and older was already approved earlier this month, after a wider majority of the panel backed that shot.

For protection in babies, another potentially groundbreaking product is scheduled to be discussed by a different FDA committee next month

After the meeting, the FDA is expected to issue its decision on approval of that so-called "passive immunization" drug, an antibody injection developed by AstraZeneca and Sanofi, by the end of September.

Currently, there is only one prevention option for RSV in babies: Biovitrum's palivizumab, branded as Synagis. But that requires monthly infusions, and is generally restricted to only babies with underlying conditions.

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