» White House to extend bans on travel.

President Joe Biden will ban travel by noncitizens into the United States from South Africa because of concern about a coronavirus variant spreading in that country and will extend similar bans imposed by his predecessor on travel from Brazil, Europe and the United Kingdom, his press secretary said Monday.

The move comes as officials in the new Biden administration are trying to get their hands around a fast-changing pandemic, with public health officials racing to vaccinate the public — and to expand the supply of vaccine — as more contagious variants of the coronavirus spread.

Dr. Anthony Fauci, the government’s leading infectious disease specialist, said at the White House last week that “we’re following very carefully” the variant of the virus in South Africa because it appears to be more highly contagious. On Monday, Moderna said its vaccine is effective against new variants of the coronavirus that have emerged in Britain and South Africa. But the immune response is slightly weaker against the variant discovered in South Africa, and so the company is developing a new form of the vaccine that could be used as a booster shot against that virus.

And Dr. Rochelle Walensky, the new director of the Centers for Disease Control and Prevention, offered a blunt assessment of the vaccination campaign Sunday, predicting that supply would not increase until late March. Federal health officials and corporate executives agree that it will be impossible to increase the immediate supply of vaccines before April because of lack of manufacturing capacity. A third vaccine maker, Johnson & Johnson, is expected to report the results of its clinical trial soon; if approved, that vaccine would also help shore up production.

Biden’s travel ban is a presidential proclamation, not an executive order; typically, proclamations govern the acts of individuals, while executive orders are directives to federal agencies. It will go into effect Saturday and apply to nonu.s. citizens who have spent time in South Africa in the last 14 days. The new policy, which was earlier reported by Reuters, will not affect U.S. citizens or permanent residents, officials said.

A White House official said Sunday that the CDC will not issue waivers from that policy as some airlines had requested.