NEW YORK • As the coronavirus assumes contagious new forms around the world, two drugmakers reported on Monday that their vaccines, while still effective, offer less protection against one variant and began revising plans to turn back a shape-shifting pathogen that has killed more than two million people.
The news underscored a realisation by scientific experts that the virus is changing more quickly than once thought, and may well continue to develop in ways that help it elude the vaccines being deployed.
Governments are rushing to dispense vaccines needed to head off an enemy showing signs that it, too, has picked up the pace.
The announcements arrived even as US President Joe Biden banned travel to the United States from South Africa, in hopes of stanching the spread of one variant. And Merck, a leading drug firm, on Monday abandoned two experimental vaccines altogether, saying they did not produce a strong enough immune response against the original version of the virus.
The vaccines made by Moderna and Pfizer-BioNTech are both effective against new virus variants discovered in Britain and South Africa, the companies said. But they are slightly less protective against the South Africa variant, which may be more adept at dodging antibodies in the blood. The two are the only vaccines authorised for emergency use in the US.
Moderna has already begun developing a new form of its vaccine that could be used as a booster shot against the variant in South Africa.
"We're doing it today to be ahead of the curve, should we need to," said Moderna's chief medical officer Tal Zaks. Moderna said it also planned to begin testing whether giving patients a third shot of its original vaccine as a booster could help fend off newly emerging forms of the virus.
Dr Ugur Sahin, chief executive of BioNTech, said his company was talking to regulators around the world about what types of clinical trials and safety reviews would be required to authorise a new version of the Pfizer-BioNTech vaccine that would be better able to head off the variant in South Africa.
Studies showing decreased levels of antibodies against a new variant do not mean a vaccine is proportionately less effective, Dr Sahin said. BioNTech could develop a newly adjusted vaccine against the variants in about six weeks, he said.
The US Food and Drug Administration has not commented on what its policy will be for authorising vaccines that have been updated to work better against new variants. But some scientists said the adjusted vaccines should not have to go through the same level of scrutiny that the original ones did. The influenza vaccine is updated yearly to account for new strains without an extensive approval process.
"The whole point of this is a rapid response to an emerging situation," said virus expert John Moore.
Dr Sahin said a similar booster shot eventually may be necessary to stop Covid-19.
Scientists had predicted that the coronavirus would evolve and might acquire new mutations that would thwart vaccines, but few researchers expected it to happen so soon. Part of the problem is the sheer ubiquity of the pathogen.
"The more people infected, the more likely that we will see new variants," said Dr Michel Nussenzweig, an immunologist at Rockefeller University in New York.
The variant identified in Britain has been found in at least 20 states in the US, but those first found in Brazil and South Africa have not yet been detected in this country.
It is far from certain that these are the only worrying variants out there. Few countries, including the US, have invested in the kind of genetic surveillance needed to detect emerging variants.
One reason the current vaccine remains effective is a "cushion effect", meaning it provokes such a powerful immune response that it will remain highly protective even with some drop in antibody strength, said Dr Anthony Fauci, Mr Biden's adviser on the coronavirus.