A COVID-19 vaccine specifically targeting the omicron variant would be "prudent" even if it ultimately may not be needed, the top U.S. infectious disease official said on Tuesday as Pfizer announced trials for such a vaccine.

"It makes sense to think in terms of at least having ready an omicron specific boost," Dr. Anthony Fauci, President Joe Biden's top medical adviser and a member of the White House COVID-19 Response Team, told MSNBC.

"We may not need it... but I think it's prudent to at least prepare for the possibility that this may be a persistent variant that we may have to face - even if it's at a very low level," he added.

Earlier on Tuesday, Pfizer Inc and its partner BioNTech SE said they have started clinical trials for a version of their vaccine targeting the highly-transmissible variant that has eluded their current two-dose protection and led to breakthrough infections.

While much of the nation is still grappling with high omicron infections even as cases subside in some states, Fauci said eventually enough community immunity will hopefully build up to prevent massive surges such as the four to five waves driven by variants so far.

"I don't think we're going to be seeing that indefinitely," he said, adding that COVID was unlikely to be eradicated.