* First tests of vaccine against new variants encouraging
* Scientists say mutations will need constant monitoring
* Variants found in South Africa, Britain; more infectious (Adds definition of spike protein, other details)
By Michael Erman
NEW YORK, Jan 7 (Reuters) - Pfizer Inc and BioNTech's COVID-19 vaccine appears able to protect against a key mutation in the highly transmissible new variants of the coronavirus discovered in Britain and South Africa, according to a laboratory study conducted by the U.S. drugmaker.
The study by Pfizer and scientists from the University of Texas Medical Branch, which has not yet been peer-reviewed, indicated the vaccine was effective in neutralizing variants with the so-called N501Y mutation, situated on a portion of the virus that it uses to enter and infect cells.
All of the vaccines already approved or in development use this outer portion of the virus, known as the spike protein, to train the body to recognize the virus and make virus-neutralizing antibodies.
The N501Y mutation is linked to greater transmissibility, and scientists have expressed concerns it could also allow the virus to escape the neutralizing antibodies produced in response to the vaccine, said Phil Dormitzer, one of Pfizer's top viral vaccine scientists.
The first results of tests on some of the key variants of concern offer some hope as Britain and other countries try to tame the more infectious variants, which authorities believe are driving a surge in infections that could overwhelm healthcare systems.
Although all viruses mutate constantly, scientists are concerned about the mutations first discovered in Britain and South Africa because they are believed to be capable of altering key functions of the virus.
The Pfizer study was conducted on blood taken from people who had been given the vaccine. Its findings are limited because it does not look at the full set of mutations found in either of the new variants of the rapidly spreading virus.
Dormitzer said it was encouraging that the vaccine appears effective against the mutation, as well as against 15 other mutations the company has previously tested.
"So we've now tested 16 different mutations, and none of them have really had any significant impact. That's the good news," he said. "That doesn't mean that the 17th won't."
The study still does not address a worrisome mutation in the South African variant, called the E484K mutation.
The U.S. researchers plan to run similar tests to see whether the vaccine protects against other mutations from the variants from Britain and South Africa. They hope to have data within weeks.
The variants are said by scientists to be more transmissible than previously dominant ones, but they are not thought to cause more serious illness.
Independent experts gave a cautious welcome to the Pfizer study findings, but said the situation needs constant vigilance.
Paul Hunter, a professor in medicine at Britain's University of East Anglia, said "the jury is still out on the impact of the South African variant on vaccine efficacy."
Deborah Dunn-Walters, a professor of immunology at Surrey University in Britain, said it was "reassuring" that Pfizer is closely monitoring variants.
Ongoing testing will be needed, experts said, to allay concerns about whether vaccines being given to millions of people in the fight against the pandemic will protect them as the virus mutates. COVID-19 has killed more than 1.8 million people worldwide.
"The evidence is not conclusive but there is a lot to indicate that the existing mRNA vaccines do cover the new variants. That is the good news," said Andreas Bergthaler, principal investigator at the Research Center for Molecular Medicine of the Austrian Academy of Sciences in Vienna.
TESTS AND TWEAKS
AstraZeneca, Moderna and CureVac are also testing whether their shots will protect against the fast-spreading coronavirus variants. They have said they expect them to be effective, but have not said when study results will be published.
The Pfizer/BioNTech COVID-19 vaccine and the one from Moderna Inc, which both use synthetic messenger RNA technology, or mRNA, can be quickly adapted to address new mutations in the coronavirus if necessary. Scientists have suggested the changes could be made in as little as six weeks.
Eleanor Riley, a professor of immunology and infectious disease at Edinburgh University, said similar studies would need to be repeated as new mutations appear. "It may be necessary to tweak the vaccine over time," she said.
A senior British lawmaker expressed concerns in an interview on Friday that COVID-19 vaccines might not work properly against the South African variant. He was not responding to questions about Friday's data.
(Additional reporting by Kate Kelland in London, Julie Steenhuysen in Chicago and Doug Busvine in Berlin; Writing by Josephine Mason; Editing by Bill Berkrot, Edwina Gibbs, Timothy Heritage and Dan Grebler)
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