Dr. Anthony Fauci, the federal government’s top infectious disease expert, acknowledged Monday that the more highly contagious coronavirus variant first detected in England also appears to be more deadly than the predominant strain that has spread throughout the world. 

Fauci’s comments on NBC’s “Today” show came three days after British Prime Minister Boris Johnson said there is "some evidence" the variant "may be associated with a higher degree of mortality." Johnson’s chief scientific adviser, however, stressed Friday there was still “a lot of uncertainty around these numbers.”

When asked by anchor Savannah Guthrie how concerning the variant is, citing the UK's evidence that it may be more deadly, Fauci replied, “taking a look at the preliminary data that the U.K. scientists have analyzed, I’m pretty convinced that there is a degree of increase in seriousness of the actual infection, which we really have to keep an eye on.”

Fauci, who is the director of the National Institute of Allergy and Infectious Diseases, said public health officials are also concerned about the South African variant because studies show that it is more resistant to monoclonal antibodies used as COVID-19 treatment. He also said there is “a very slight, modest diminution” in vaccine response to the strain.

“But I don’t want people to think at this point that the vaccines are not effective against them [the variants]. They are,” said Fauci, who is also President Joe Biden’s chief medical adviser. 

Fauci added that scientists are already taking steps to upgrade vaccines anyway.

Moderna said Monday that its COVID-19 vaccine is effective against the new variant strains. The company added it is launching two new studies, including one into a third shot that would boost the two-dose routine of the vaccine, as well as advancing a new vaccine specific to the variant.

Coronavirus numbers are finally trending in the right direction in the U.S. For the first time since November, the country has gone seven straight days with fewer than 200,000 new reported cases, according to data compiled by Johns Hopkins University.  And the number of hospitalizations, which peaked at 132,474 on Jan. 6, was down to 110,628 on Sunday, according to The COVID Tracking Project.

Fauci is not crediting vaccinations yet for the falling numbers, instead calling it “the natural course of plateauing.” He added that Americans should continue to take the virus seriously and follow public health guidelines such as social distancing and mask wearing. 

“We don’t want to get complacent and think, ‘Oh, things are going in the right direction. … If the [U.K.] variant that has greater degree of transmissibility becomes dominant, we’re going to be faced with another challenge of a virus that has a more efficient capability of spreading,” he said.