A mutation of coronavirus able to spread more easily may have emerged, America’s top infectious disease expert has warned as Texas made mask-wearing in public mandatory.
Dr Anthony Fauci, who sits on the White House coronavirus task force, said there is data to suggest the existence of a new mutation of Covid-19 which is more “transmissible”.
He cautioned that scientists are still trying to confirm its existence and it does not appear to be more damaging for people who catch that version.
However the potential existence of a mutation which spreads more easily is a cause for concern as the United States grapples with record highs of new daily coronavirus cases.
Texas, one of the states seeing a surge in both case numbers and hospitalisations, announced new restrictions ordering the use of face masks in certain situations.
Texans in counties with 20 or more Covid-19 cases - the vast majority of the state - must have their nose and mouth covered in outdoor public spaces or a building open to the public.
Some exceptions were listed included for children who are under 10 years old or people who are exercising, eating or drinking outdoors.
Greg Abbott, the Republican governor of Texas, said that if the state wanted to make sure businesses can stay open - a call heard often from the White House - it was vital to stop the virus’s spread.
The move comes with a recent flurry of senior Republicans urging Americans to wear face masks in public as the virus surges in the country.
Mitch McConnell, the top Republican in the Senate, and Steven Mnuchin, the Treasury secretary, issued public calls for people to do so in recent days.
Donald Trump also said he was “all for masks” and joked that he looked like the Lone Ranger when wearing one in a recent interview, adopting a less critical tone than at times in the past.
Yet his plan last night to attend a July 4 celebration at Mount Rushmore, where four past presidents are carved into a cliff in South Dakota, came in for criticism.
The event, due to feature a fireworks display, was expected to be attended by 7,500 people.
Face masks were going to be handed out but attendees were not required to socially distance themselves from others.
Kristi Noem, the state's Republican governor, told Fox News that social distancing would not be needed at the event so people can “enjoy the freedoms and liberties in this country".
Dr Fauci made his comments about a new mutation of Covid-19 during an appearance on a podcast run by The Journal of the American Medical Association.
“I think the data is showing that there is a single mutation that actually makes the virus be able to replicate better and maybe have high viral loads,” Dr Fauci said.
“We don't have a connection to whether an individual does worse with this or not. It just seems that the virus replicates better and may be more transmissible.”
Dr Fauci, the director of the National Institute of Allergy and Infectious Diseases, added that confirmation was still being sought and that “very good” scientists continued to work on the issue.
Viruses naturally mutate and scientists have previously found evidence of minor mutations of Covid-19 which have not changed its ability to spread or harm people.
The World Health Organisation has gathered samples taken from across the world and is monitoring more than 60,000 different genetic sequences of coronavirus.
In America some 55,000 new cases of Covid-19 were confirmed on Thursday, yet again a record high. That is around 20,000 more cases than the first peak in April.
Now 36 of the 50 US states are seeing cases rise, according to a CNN tracker. The surge has seen parts of the country that had been reopening go into reverse.