The U.S. Centers for Disease Control and Prevention is stepping up efforts to track coronavirus mutations and keep vaccines and treatments effective against new variants until collective immunity is reached, the agency’s chief said.

The United States’ daily death toll from Covid-19 surpassed 3,000 for the first time, prompting pleas for Americans to scale back Christmas plans even with vaccines on the cusp of winning regulatory approval.

U.S. health officials and politicians pleaded with Americans to stay at home over the Thanksgiving holiday and abide by constraints placed on social and economic life as record coronavirus caseloads pushed hospitals to their limits.

U.S. President Donald Trump said in a Fox News interview he no longer has Covid-19 and is not a transmission risk for the virus, as he prepares to hit the campaign trail with a return to big rallies.