Prime Minister Boris Johnson of Britain's scientific advisers urged restraint in interpreting preliminary evidence about the variant.

Dr. Anthony S. Fauci, President Biden's chief medical adviser for Covid-19, addressed reporters from the White House on Thursday, and warned the nation was 'still in a very serious situation' because of the pandemic.

In his first official full day in office, President Biden provided an update on his administration's Covid-19 response.

A limited supply of available vaccine doses has affected New York's Covid-19 vaccination efforts, with Gov. Andrew M. Cuomo saying the state will temporarily run out of vaccine in the next few days.

Vice President Kamala Harris swore in three new senators Wednesday: Jon Ossoff and the Rev. Raphael Warnock of Georgia, and Alex Padilla of California. Democrats now have narrow control of the Senate.

The head of the World Health Organization says that the promise of equitable access to the vaccines 'is at serious risk.'

After recovering from a near-fatal poisoning in Germany, the Russian opposition leader Aleksei A. Navalny returned to Moscow on Sunday and was detained at the airport.

President-elect Joseph R. Biden Jr. and Vice President-elect Kamala Harris introduced key members of their White House science team on Saturday.

India's campaign to inoculate its population of 1.3 billion began on Saturday with medical workers. The country has reported more than 10.5 million coronavirus cases, the second largest caseload after the United States.

President-elect Joseph R. Biden Jr. called the current vaccine rollout a 'dismal failure' and vowed to move aggressively to increase availability, improve access and accelerate production of needed supplies.