Advisers to the U.S. Food and Drug Administration on Thursday backed the safety and effectiveness of Pfizer Inc'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.

(Reporting by Mariam Sunny and Raghav Mahobe in Bengaluru; Editing by Bill Berkrot)