New variants of the coronavirus circulating globally appear to increase transmission and are being closely monitored by scientists.

Driving the news: The highly contagious variant B.1.1.7 originally detected in the U.K. could become the dominant strain in the U.S. by March if no measures are taken to control the spread of the virus, the Centers for Disease Control and Prevention said Friday.

Why it matters: Countries are being overwhelmed by surges in cases that have led to border closures, quarantines and more aggressive pushes for the public to get vaccinated. So far, the variants do not appear to be resistant to the existing vaccines or cause more severe disease.

The state of play: Public officials are tracking SARS-CoV-2 variants, including the B.1.1.7 variant detected in the U.K., the 501.V2 variant in South Africa and a newly discovered variant in Brazil.

The B.1.1.7 variant has been identified in about 45 countries, but nations without routine genetic surveillance, including the U.S., may not fully know the extent of the spread, sparking calls for increased monitoring.

• Public Health England released a new study of B.1.1.7 that estimated the variant is 30% to 50% more transmissible than other forms of the virus.
• 12 U.S. states have detected the B.1.1.7 variant. The CDC estimates it's linked to about less than half a percent of cases in the U.S. so far and isn't the dominant variant.

The 501.V2 variant is "a little bit more concerning regarding the possibility of interfering with some of the monoclonal antibodies," based on preliminary findings, top infectious disease expert Anthony Fauci told Axios last week.

• The variant carries a number of mutations that show changes to some of the virus' spike protein, which experts say is cause for concern since the spike protein is what coronavirus uses to gain entry into human cells, BBC reports.

Japan’s Health Ministry detected a variant on Sunday after travelers returned from Brazil. There are still many unknowns, but scientists say it has 12 mutations and studies are underway into the efficacy of vaccines against the new variant.

• Brazil's Health Ministry has asked Japan for information such as the genetic sequence of the new strain, according to the Japan Times.

The big picture: Viruses mutate, often without impacting the severity of disease or how the virus spreads. But sometimes mutations are consequential for public health and scientists say it's important to monitor them.

• Both Pfizer and Moderna are in the process of testing their vaccines against the variants. Pfizer and BioNTech said Thursday the mutation N501Y found in both variants B.1.1.7 and 501.V2 was tested against their vaccine and found “no reduction in neutralization activity against the virus.”
• But there are multiple mutations and more studies are underway.

What to watch: On Friday, CDC officials pushed back on reports of a U.S. variant of the virus, the New York Times reports.

• “To date, neither researchers nor analysts at CDC have seen the emergence of a particular variant in the United States,” the CDC said.
• The White House did not immediately respond to a request for comment.

The bottom line: Viruses mutate and evolve and the coronavirus is no different. So far, public health officials still say wearing a mask, socially distancing, testing and contact tracing, and hand washing are best practices for stopping the spread of COVID-19.