* UK says worried about S.African variant
* Mutations include extensive alterations to spike protein
* Changes could lead to "escape from immune protection"
* Vaccine makers are testing shots against new variants (Recasts with quotes, details from scientists)
LONDON, Jan 4 (Reuters) - UK scientists expressed concern on Monday that COVID-19 vaccines being rolled out in Britain may not be able to protect against a new variant of the coronavirus that emerged in South Africa and has spread internationally.
Both Britain and South Africa have detected new, more transmissible variants of the COVID-19-causing virus in recent weeks that have driven a surge in cases. British Health Secretary Matt Hancock said on Monday he was now very worried about the variant identified in South Africa.
Simon Clarke, an associate professor in cellular microbiology at the University of Reading, said that while both variants had some new features in common, the one found in South Africa "has a number additional mutations ... which are concerning".
He said these included more extensive alterations to a key part of the virus known as the spike protein - which the virus uses to infect human cells - and "may make the virus less susceptible to the immune response triggered by the vaccines".
Lawrence Young, a virologist and professor of molecular oncology at Warwick University, also noted that the South African variant has "multiple spike mutations".
"The accumulation of more spike mutations in the South African variant are more of a concern and could lead to some escape from immune protection," he said.
Scientists including BioNTech CEO Ugur Sahin and John Bell, Regius Professor of Medicine at the University of Oxford, have said they are testing the vaccines against the new variants and say they could make any required tweaks in around six weeks.
Public Health England said there was currently no evidence to suggest COVID-19 vaccines would not protect against the mutated virus variants. Britain's health ministry did not immediately respond to requests for comment.
The world's richest countries have started vaccinating their populations to safeguard against a disease that has killed 1.8 million people and crushed the global economy.
There are currently 60 vaccine candidates in trials, including those already being rolled out from AstraZeneca and Oxford, Pfizer and BioNTech, Moderna, Russia's Sputnik V and China's Sinopharm .
Scientists say both the South African and UK variants are associated with a higher viral load, meaning a greater concentration of virus particles in patients' bodies, possibly contributing to increased transmission.
Oxford's Bell, who advises the UK government's vaccine task force, said on Sunday he thought vaccines would work on the British variant but said there was a "big question mark" as to whether they would work on the South African variant.
BioNTech's Sahin told Germany' Spiegel in an interview published on Friday that their vaccine, which uses messenger RNA to instruct the human immune system to fight the virus, should be able to protect against the UK variant.
"We are testing whether our vaccine can also neutralise this variant and will soon know more," he said. (Reporting by Kate Holton, Kate Kelland, Guy Faulconbridge and Alistair Smout; Editing by Mike Collett-White)
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