By Sneha S K

May 6 (Reuters) - Moderna's ( MRNA ) mRNA-based seasonal

flu vaccine worked better than conventional flu shots in a

late-stage international trial of more than 40,000 adults aged

50 and older, researchers reported on Wednesday.

The vaccine is currently under review by the U.S. Food and

Drug Administration after the agency rejected the company's

initial application. A decision is expected by August 5.

If approved, Moderna's ( MRNA ) shot would be the first seasonal flu

shot in the United States made with mRNA technology, a faster

vaccine platform than conventional methods, but one Health

Secretary Robert F. Kennedy Jr. has targeted for extra scrutiny.

Kennedy, a long-time anti-vaccine activist, has been

particularly critical of mRNA technology, canceling hundreds of

millions in research funding and making claims not backed by

scientific evidence.

In the study, Moderna's ( MRNA ) flu shot was 26.6% more effective

than an approved standard-dose flu shot from GSK,

exceeding the study's main goal of showing the shot was at least

as good as existing vaccines.

"These findings support the role of mRNA-1010 in improving

influenza prevention," Dr. Isabel Leroux-Roels of Ghent

University and colleagues wrote in the study published in the

New England Journal of Medicine.

Side effects, including injection-site pain, fatigue,

headache and muscle aches, were more common with the Moderna ( MRNA )

shot compared with the standard flu shot, but most were mild to

moderate and short-lived.

Severe side effects were balanced between the two groups,

occurring in 2.2% of those who received the mRNA shot and 1.9%

with the standard dose vaccine, researchers reported.

Overall, safety was consistent with findings from prior

late-stage trials, the study authors said.

In February, the FDA rejected Moderna's ( MRNA ) application, citing

concerns about the standard dose flu shot used in the comparison

group. The agency argued that the company should have tested its

shot against a high-dose flu vaccine in people aged 65 and

older, which is recommended in the United States because of its

higher efficacy.

After meeting with the company, the agency reversed course

and accepted an amended application with the promise that

Moderna ( MRNA ) would conduct an additional study in older adults once

the vaccine is approved.

Regulatory reviews for Moderna's ( MRNA ) flu shot are also underway

in the EU, Canada and Australia.

The company's combined mRNA flu and COVID-19 vaccine won

European Commission approval in April.