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The scientific and pharmaceutical race to keep coronavirus vaccines ahead of new virus variants escalated Monday, even as a highly transmissible variant first detected in people who had recently traveled to Brazil was discovered in Minnesota.

Moderna, the maker of one of the two authorized coronavirus vaccines in the United States, announced it would develop and test a new vaccine tailored to block a similar mutation-riddled virus variant in case an updated shot becomes necessary.

The effort is a precautionary step. Evidence released Monday suggested that the Moderna vaccine will still work against two variants of concern that emerged in the United Kingdom and South Africa. The plan highlights that the scientists who responded with unprecedented speed and success to develop coronavirus vaccines are already moving to address new challenges. It also amplifies the urgency of getting as many people immunized with current vaccines as quickly as possible.

“We need to double down on public health measures. The less a virus spreads, the less it’s going to mutate,” said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases. “We need to get as many people vaccinated with the current vaccine that we have as we possibly can … and prepare for the potential eventuality that we might have to update this vaccine sometime in the future.”

The success of two remarkably effective coronavirus vaccines from Moderna and Pfizer-BioNTech in record time last year provided breathing room and hope, even as the pandemic surged. But the detection of variants in the United Kingdom, South Africa and Brazil in recent weeks raised immediate concern.

Those variants, each with a different assemblage of mutations, spread much more easily. But some of the mutations in each variant drew special concern because they sit in the spiky proteins that dot the outside of the coronavirus and have been the key target for vaccines and therapeutics.

The British variant has been detected in the United States at least 130 times, and Minnesota public health officials announced Monday that they had detected the Brazilian variant, which some reports suggest may be able to evade natural immunity, allowing people to become reinfected. The Minnesota Department of Health said the case involved a resident with recent travel history to Brazil.

The emergence of the variants raised the specter that the current generation of vaccines might be rendered obsolete before they have even been fully rolled out.

The emerging evidence, though still partial, puts some of those fears to rest. The study released Monday, before peer review, suggests the Moderna vaccine will probably protect against variants first detected in Britain and South Africa. A Pfizer-BioNTech study released last week found that its vaccine probably protects against the British variant. Those findings add to a growing body of experiments testing antibody-rich blood serum from vaccinated people against new mutations, with largely encouraging results.

But the study of the Moderna vaccine contains a clear warning sign: Although the disease-fighting antibodies appeared to work against the South African variant, that efficacy was diminished. That prompted the company to design a new potential vaccine that could be added to the current two-dose regimen if needed, which will soon be tested in human trials. Moderna will also test a third dose of its current vaccine to see whether revving up a person’s immune response against the original version of the coronavirus could help protect against the variant.

“The virus is changing its stripes, and we will change to make sure we can beat the virus where it’s going,” Moderna President Stephen Hoge said in an interview. “The unknown is: Would we feel it’s necessary to do that, would public health officials want this at that point or would they still be comfortable? What we’re trying to do is create an option.”

Janet Woodcock, acting commissioner of the Food and Drug Administration, said in an interview Monday that the agency understands the urgency of dealing with the potential problems posed by new variants. She said the utility of vaccines, monoclonal antibody treatments and some coronavirus tests “could be undermined” if there is a big enough change caused by a new coronavirus strain.

Woodcock said the FDA is in talks with manufacturers about how to deal with the threat. New FDA policies on how to test for efficacy involving a new variant, she said, would be made public because of intense interest.

Woodcock stressed that the variants problem showed why a global response is so important. Unless the coronavirus is eradicated everywhere, she said, it will remain a threat to the United States and other countries.

The emerging evidence shows the need to deploy current vaccines as quickly as possible, a campaign that has accelerated markedly in the United States over the past week, with more than 1 million shots given each day since last Tuesday, according to Washington Post data. It also underscores the importance of vigilance, to fully investigate any cases of the coronavirus that develop in people who are vaccinated so that there is an early alert if the virus shows it can break through the immunity conjured by vaccines.

A growing number of scientists anticipate the potential need for periodic reboots of the coronavirus vaccines, similar to an annual flu shot, to deliver a boost of immunity tailored to closely match new variants.

The vaccines “are still going to be highly effective, and they are probably the most important tools we have to get this thing under control,” said Ravindra Gupta, a professor of clinical microbiology at the University of Cambridge’s Institute of Therapeutic Immunology and Infectious Disease, who found in a study of older adults that the immune response triggered by the Pfizer-BioNTech vaccine was modestly less effective against the British variant. “With flu, we need to adapt the vaccines. We can see that already. The companies do realize there is a problem in the longer term, and they will deal with it just as we have done with flu every year.”

In the Moderna study, antibody-containing blood serum taken from people and monkeys who received the vaccine was tested against “pseudoviruses” that are engineered to contain the spike protein present in the U.K. and South African variants. The serum was able to block both viruses and remained above a threshold of efficacy for the South African variant, despite a diminution in effectiveness.

Barney Graham, deputy director of the Vaccine Research Center at the National Institutes of Health and an author of the study, said more experiments are forthcoming that will help guide public health experts’ thinking. But he speculated, based on his knowledge of other viruses, that the evidence so far is that the current vaccines will still work.

“I think we’re okay for now, but [the virus] is changing,” Graham said. “It means that if some of these mutations accumulate to a certain extent, you may end up with a new strain that’s not protected by the vaccine, so all of this is being done out of an abundance of caution.”

There have also been reminders that although the first two vaccines worked remarkably well, success is not guaranteed in vaccine development. Merck, a longtime vaccine company, made the surprising announcement Monday that it was abandoning two vaccine candidates after early human studies showed that both triggered inferior immune responses compared with other vaccines and natural infection.

The Merck effort started later and significantly lagged other companies, and the nation’s vaccination plan wasn’t heavily reliant on a possible Merck shot. The two authorized vaccines use a novel approach that had never been used in an authorized vaccine, while Merck employed a more traditional approach.

Late last year, Sanofi and GlaxoSmithKline announced they were redesigning their vaccine after a first version did not cause a robust immune response in older adults. After the setback, their candidate is not expected to be available until the end of this year.

Public health officials are eagerly awaiting the data from Johnson & Johnson’s trial, which could come in the next week. That data may suggest how a vaccine performs against the variant, because since some of the trial was conducted in South Africa.

The Moderna and Pfizer-BioNTech vaccines are especially well suited to rapid updates. Both use genetic material called messenger RNA that acts much like software, instructing the body’s cells how to build the spike protein found on the outside of the coronavirus. To update the vaccines, scientists have to rewrite the software to block the new target.

Hoge said the regulatory pathway for a new version of the vaccine is not entirely clear, but he does not anticipate having to run large trials with tens of thousands of volunteers, as was done to show the first vaccine was effective and safe. Instead, he said he anticipates a rebooted vaccine could be tested in hundreds or thousands of people to establish safety and that the right immune response is being triggered.

It would be possible, Hoge said, to begin making a new vaccine at large scale by the summer.

Pfizer, partnering with BioNTech, and Moderna have created promising vaccines that scientists hope will lead to more medical breakthroughs using mRNA. (Joshua Carroll, Brian Monroe/The Washington Post)

Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said trying to extrapolate from laboratory experiments to understand whether vaccines would still be protective was like trying to read tea leaves, because it isn’t yet known what level of antibodies protects someone against the virus. But he pointed out that the immune system musters a multipronged defense, and the laboratory tests conducted so far don’t capture the entirety of the response.

“I would say we don’t need to worry about this until it has shown to be a problem,” Offit said. “That said, we should prepare for it to be a problem.”

Monoclonal antibody treatments are more likely to be ineffective against new variants because they use only one piece of the body’s immune response.

The FDA’s Woodcock said that monoclonal antibodies are “fairly sensitive” to changes in the virus and that the companies making them and the government are testing the treatments against various strains. She said the South African variant might pose a threat to one of the antibody treatments but that “we have a whole stream” of antibodies, including some that are cocktails, under development.

Former FDA commissioner Mark McClellan said the key to the United States staying ahead of the mutations is through surveillance by genomic sequencing.

“If you have a good surveillance system,” McClellan said, “you can identify the variants before they spread widely.”