April 9 (Reuters) - Pfizer ( PFE ) said on Tuesday its

respiratory syncytial virus (RSV) vaccine Abrysvo was well

tolerated and generated an immune response in higher risk adults

under the age of 60 similar to that in older adults, for whom

the shot is already approved.

Pfizer ( PFE ) said it plans to submit its findings from the trial

to seek expanded approval of the vaccine in adults ages 18 to

59, but did not give a time frame for when it expects the data

to be considered by regulators.

"This represents a real opportunity for an expansion to an

age population in a risk population that wouldn't normally see

the availability of this vaccine so soon," Dr. Iona Munjal,

executive director of clinical vaccine R&D at Pfizer ( PFE ), said in an

interview.

The U.S. drugmaker last year launched Abrysvo for older

adults and for pregnant women to protect their babies from the

virus. GSK also launched its rival vaccine Arexvy in

2023 and has dominated the RSV vaccine market over the first

season they were available.

The British drugmaker is also looking to expand the age

range for its shot and has already submitted data for adults

ages 50 to 59 to the U.S. Food and Drug Administration. The FDA

is expected to decide on whether to approve the label expansion

by June 7, which could allow GSK to offer its shot in the

younger age group later this year.

Pfizer ( PFE ) did not say whether it expects to be able to expand

Abrysvo's label in time for the 2024-25 respiratory virus

season.

RSV, which typically causes cold-like symptoms, is a leading

cause of pneumonia in toddlers and older adults.

The late-stage trial of Pfizer's ( PFE ) shot involved 681 adults

aged 18 to 59 with conditions including asthma, diabetes, and

chronic obstructive pulmonary disease that increase the risk

from RSV. In this group, the immune response was non-inferior to

the one observed in older adults, Pfizer ( PFE ) said.

The company said those with a higher risk profile represent

9.5% of U.S. adults 18 to 49 years of age and nearly a quarter

of those between the ages of 50 and 64.

Dr. David Boulware, an infections disease specialist at the

University of Minnesota, said he was not sure most Americans who

fit those high risk categories would need the shot.

People who have had organ transplants, are undergoing

chemotherapy for cancer, or are survivors of congenital disease

would clinically benefit from the shot, he suggested.

"The clinical benefit is likely going to be relatively low

for most people," he said.