June 12 (Reuters) - The U.S. Food and Drug

Administration on Thursday expanded the use of Moderna's ( MRNA )

respiratory syncytial virus vaccine to a lower group of

adults aged 18 to 59 years at increased risk for disease.

Moderna's ( MRNA ) RSV shot, mRESVIA, was the first non-COVID-19

messenger RNA-based (mRNA) vaccine to be approved in the United

States. The shot, the company's second product, is already

approved for the prevention of RSV-associated lower respiratory

tract disease in adults aged 60 or older.

While the FDA approval is a necessary step, the U.S. Centers

for Disease Control and Prevention still has to recommend the

shots before they are available for the age group.

The CDC currently recommends the vaccine for adults aged 75

and older, as well as for adults aged 60 to 74 who are at

increased risk of infection.

In April, the CDC's panel of outside experts recommended the

use of approved RSV vaccines in at-risk adults aged 50 to 59.

Health Secretary Robert F. Kennedy Jr. on Wednesday named

eight new members to serve on the key panel of vaccine advisers,

known as the Advisory Committee on Immunization Practices, after

previously firing all 17 of its members, saying it would

"re-establish public confidence in vaccine science."

However, public health experts warn that this could

undermine public confidence in available vaccines.

Some of the new appointees have openly expressed

anti-vaccine views, including against the mRNA vaccine

technology.

The panel, which provides guidance to the CDC on which

groups of people would most benefit from an already-approved

vaccine, is scheduled to meet later this month.

RSV typically causes cold-like symptoms, but is also a

leading cause of pneumonia in toddlers and older adults. The CDC

estimates 15,000-20,000 annual RSV-associated hospitalizations

in the U.S. in adults aged 50 to 59.

The FDA's approval for mRESVIA was based on results from a

late-stage trial where the shot helped initiate significant

immune responses in adults aged 18 to 59 years with underlying

health conditions.

The vaccine was well-tolerated with no safety concerns, the

company said.

The FDA approved mRESVIA in adults aged 60 or older last

year, but with a lower efficacy label indicating the shot was

79% effective at preventing at least two symptoms of RSV, such

as cough and fever. Moderna ( MRNA ) had said the shot was shown to be

83.7% effective in a late-stage trial.

All currently approved shots against RSV, including Pfizer's ( PFE )

Abrysvo and GSK's Arexvy, are for adults aged 60

years and above.

Arexvy and Abrysvo are also approved to prevent

RSV-associated disease in at-risk adults aged 50 to 59 and 18 to

59, respectively.