He’s not cow-ering over mu.

Dr. Anthony Fauci said Thursday that the U.S. is closely monitoring the new so-called “mu” coronavirus variant, which is feared to evade vaccine-based immunity, but that the strain doesn’t seem to pose an “immediate threat.”

The variant, which is also called B.1.621 and was first spotted in Colombia in the winter, was designated by the World Health Organization as a variant of interest on Monday.

“We certainly are aware of the mu variant — we are keeping a close eye on it,” Fauci, America’s top infectious disease expert, said in a virtual news briefing.

But he stressed that the strain is still a minor player in the nation’s coronavirus fight, with the delta variant accounting for more than 99% of cases.

Fauci says the new Mu variant of COVID is “not at all even close to being dominant” and not considered “an immediate threat.” He says laboratory data suggests Mu could evade some vaccines, but there isn’t much clinical research yet and vaccines are likely still “quite effective” pic.twitter.com/hgDlkLfTyd

— CBS News (@CBSNews) September 2, 2021

He said the mu variant has mutations that suggest that it could dodge some vaccine-generated antibodies. But there is no significant clinical data showing it stumps immunizations, he noted.

“We take it very seriously,” Fauci said. “But remember, even when you have variants that do diminish somewhat the efficacy of a vaccine, the vaccines still are quite effective against variants of that type.”

Fauci also said that, based on his experience with infectious diseases, he believes a third dose of mRNA vaccines, namely Pfizer and Moderna, will be required to provide long-term protection against COVID. The U.S. is still studying the need for a booster dose of the single-shot Johnson & Johnson vaccine.

“I must say from my own experience as an immunologist, I would not at all be surprised that the adequate full regimen for vaccination will likely be three doses,” Fauci told reporters during a White House COVID briefing.

A formal determination of the third dose for “full vaccination’” would have broad implications for schools, businesses and other entities with vaccine mandates.

White House COVID coordinator Jeff Zients says the federal government will bring the “same intensity” to encouraging Americans to get booster shots as it did for the initial vaccination campaign.

The infectious disease expert’s comments come as the Biden administration prepares to begin widely distributing COVID booster shots the week of Sept. 20.