LONDON (AP) — British health authorities were aiming to vaccinate 15,000 people at London's Twickenham rugby stadium on Monday as part of a race to contain a fast-spreading coronavirus variant.

The strain, first identified in India, accounts for a majority of new cases in the U.K., which is seeing a rise in infections after weeks of decline. Scientists say the variant is more transmissible than the U.K.'s previously dominant strain, but current vaccines appear to be effective against it.

Many scientists are urging the U.K. government to delay plans to lift social distancing rules and other remaining restrictions on June 21, arguing that more people need to be vaccinated before measures can be eased safely.

The government says it will announce on June 14 whether the relaxation will be delayed.

The U.K. has recorded almost 128,000 coronavirus deaths, the highest toll in Europe, but a mass vaccination campaign that started in December has brought confirmed new infections and daily deaths down sharply. Three-quarters of U.K. adults have had one dose of a coronavirus vaccine, and almost half have had both doses.

Ravi Gupta, a member of a committee that advises the government on respiratory diseases, said it would be wise to delay the June 21 reopening "by a few weeks."

"We are not too far from reaching the sort of levels of vaccination that would help us contain the virus," he told the BBC. "If you look at the costs and benefits of getting it wrong, I think it is heavily in favor of delay."

The walk-in vaccination center at Twickenham — home of England's national rugby team — was offering first jabs without an appointment on Monday to people from northwest London, a hotspot for the variant first found in India.

Health officials in the northwest England town of Bolton, which had the highest rates of the new variant, say infections are starting to fall after a mass testing and "surge vaccination" campaign there.

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