By Julie Steenhuysen

Viruses mutate frequently, and several mutated viruses have been identified. The presence of the South African variant in the United States is especially concerning because several laboratory studies have shown that it reduces vaccine effectiveness.

Another concern, according to the nominee for U.S. surgeon general, is that the South African variant could require larger doses of antibody for treatment.

“The thing that’s troublesome now that we really need to keep our eye on are these variants,” Anthony Fauci, the leading U.S. infectious disease specialist, said in an interview on MSNBC. “The one that is of greater concern and that really could be problematic is the mutant that is now dominant in South Africa.”

So far, vaccines made by Moderna Inc and Pfizer Inc /BioNTech appear protective against this variant of the coronavirus, despite the weaker response. The companies this week said they are considering making new versions of their shots just in case. Moderna also plans to test giving a third shot of its vaccine to bolster antibody levels.

The U.S. Centers for Disease Control and Prevention said in a statement that it is aware of the cases and noted that there is no evidence the variant causes more severe disease.

The arrival of the South African variant follows predictions by the CDC this month that a more-transmissible U.K. variant could become the dominant strain in the United States by March.

The South Carolina Department of Health and Environmental Control said the two cases of the B.1.351 variant of South African origin appear to be unrelated to one another.

The department said neither of the two adults had a travel history that would account for the infection.

Although the variant has been detected in more than 30 countries, the South Carolina cases were the first in the United States, it said.

“I’m very worried about the variants, all of them, all have the potential to be much more transmissible than the current version of COVID that we seem to be dealing with in the United States,” U.S. Surgeon General nominee Vivek Murthy said in a Washington Post interview.

The CDC has said the arrival of more transmissible coronavirus variants emphasizes the need for rapid rollout of the vaccine to limit the ability of the virus to continue mutating.

Fauci said the U.S. had a “very serious issue” in the number of infections but was seeing some good news in plateauing cases and efforts to ramp up vaccinations.

Another variant originally detected in the United Kingdom, called B.1.1.7, has been detected in at least 28 states, according to CDC data.

(Reporting by Peter Szekely in New York and Julie Steenhuysen in Chicago; additional reporting by Vishwadha Chander and Manojna Maddipatla in Bangalore; Susan Heavey in Washington; Peter Henderson in Oakland; Editing by Chizu Nomiyama, David Gregorio and Andrea Ricci)