May 22 (Reuters) - The U.S. Food and Drug

Administration's advisory panel is set to vote on Thursday to

recommend whether COVID-19 vaccines for the 2025-2026

immunization campaign should target strains of the virus

descending from the JN.1 variant.

According to the Centers for Disease Control and Prevention,

the LP.8.1 strain - a subvariant of the previously recommended

JN.1 strain - accounted for 70% of total cases in the U.S. over

a two-week period ended May 10.

While the LP.8.1 is the predominant circulating strain,

other virus subvariants, including LF.7 and XFG, have also been

increasingly detected in recent weeks,

FDA documents showed earlier this week.

Public health experts say that there is no certainty on

which strains are going to be dominant. The strain selection

process is "intelligent guesswork," Sten Vermund, dean of the

University of South Florida College of Public Health, told

Reuters ahead of the advisory committee meeting.

Top U.S. vaccine regulator Vinay Prasad and FDA Commissioner

Marty Makary, both of whom have been critical of U.S. COVID

vaccine policies, said the benefit of repeated annual shots for

healthy adults remains uncertain after several years of the

virus circulation and vaccine availability.

Earlier this week, the FDA said it plans to require new

clinical trials for approval of annual COVID-19 boosters for

healthy Americans under age 65.

"You would need a huge clinical trial that is very costly

and you wouldn't finish it in time for the COVID virus season,"

Vermund told Reuters.

FDA's Prasad said he was open to hearing the thoughts of the

vaccine advisory panel on the new policy.

Analysts have said the new clinical trials are reasonable

and may help alleviate investor concerns regarding vaccine

manufacturers as they maintain the existing framework for older

adults and at-risk individuals, who are typically the ones

seeking vaccinations.