By Raghav Mahobe and Mariam Sunny
(Reuters) -Advisers to the U.S. Food and Drug Administration on Thursday backed the safety and effectiveness of Pfizer Inc (NYSE:PFE)'s experimental respiratory syncytial virus (RSV) vaccine, boosting its chances of becoming the first available maternal shot to protect babies from the illness.
The FDA's advisory committee voted unanimously that available data supported the vaccine's efficacy for giving the shot to women in their second or third trimesters of pregnancy to prevent lower respiratory tract infection and severe disease in infants up to 6 months of age.
The expert panel voted 10-4 that the data also supports the safety of the vaccine for that patient population, paving the way for likely U.S. approval.
Infants are among those at greatest risk for severe illness from RSV. An estimated 58,000 to 80,000 children below the age of five years are hospitalized due to RSV infection annually in the United States, according to government data.
The FDA, which is not obligated to follow the recommendations of the advisory panel but usually does, is expected to make an approval decision by August.
The FDA's staff reviewers on Tuesday deemed the safety data for Pfizer's vaccine "generally favorable".
If approved, the U.S. Centers for Disease Control and Prevention (CDC) will then need to sign off on its use to make it widely available to pregnant mothers.
Pfizer is counting on new medicines and vaccines to help offset declining revenue from its COVID-19 products.
Though FDA staffers flagged a higher number of pre-term births among participants taking the Pfizer shot in a clinical trial compared to those who received a placebo, the FDA said the difference was not statistically significant, so that may have occurred by chance.
But some panelists expressed concern about the potential link.
"I worry that if preterm births are in anyway a consequence of this vaccine that would be tragic in many ways," said Paul Offit, director of vaccine education center at the Children's Hospital of Philadelphia, who was one of the no votes on safety.
Dr. Daniel Feikin, a respiratory diseases specialist and temporary voting member of the panel, was less concerned. "I'm not convinced that there's a clear causal relationship between this vaccine and preterm birth," he said.
Demand for a maternal RSV vaccine could be limited compared to other childhood vaccinations that are often mandated for attending schools, said pediatric expert on RSV Dr. Jonathan Miller of Nemours Children's Health, ahead of the meeting.
While there is no maternal RSV vaccine available in the United States, GSK Plc earlier this month became the first to secure U.S. approval of an RSV shot for older adults. The FDA is expected to decide on Pfizer's vaccine for the older age group later this month.
Pfizer has said it is ready to launch its RSV vaccine for both older adults and pregnant women in the United States and Europe later this year. Analysts have estimated the market for RSV vaccines to surpass $10 billion by 2030.
Data from the Pfizer vaccine's late-stage trial had shown it was 82% effective in preventing severe infections in infants when given to expecting mothers in the second half of their pregnancy.
"If the vaccine actually lives up to the data that we've seen today. I can guarantee that many infants and their parents will breathe easier in the coming years," said Jay Portnoy, one of FDA panelists.