"They are a worry".
Recently, health experts said that the double mutant variant may be less risky than expected as the most vulnerable patients are having only mild illnesses.
The Kent (UK) variant (also known as B117) remains the dominant variant in Britain.
Variations of the virus crop up all the time and when cases first appear it is hard to tell if they are significant or not, or whether there is any trend.
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She told The Independent: "The problem with this variant is that, not only does it have mutations that can evade antibodies, but they've found that it can also evade T-cells".
Prof Altmann said the discovery of the Indian variant in the United Kingdom should warrant India being placed on the UK's "red list" so all those arriving into the United Kingdom from India are required to quarantine in a hotel.
A similar delay happened before testing started to pick up the South Africa variant.
Cases of B.1.617 variant are responsible for second wave in India.
"This virus variant is a variant of interest, the B1617 lineage".
On Friday, India added a record 2,17,353 new coronavirus infections in a day, taking the total tally to 1,42,91,917 (14.2 million/1.42 crore), the Union Health Ministry said.
Dr Simon Clarke, a microbiologist at Reading University, said at the time: 'As for the L452R mutation, we're still waiting for a proper definition of what it does'.More news: At least 8 killed in mass shooting at Indianapolis FedEx facility
Officials said "all appropriate public health interventions will be undertaken, including enhanced contact tracing" after its detection, with PHE and global partners monitoring the situation "closely".
He told BBC Radio 4's PM that he thought "we should be terribly concerned about it" and that the discovery "ought" to shift India on to the Government's "red list" of countries where a hotel quarantine is required.
'We keep it under constant review and we won't hesitate to introduce tougher restrictions and add countries if we think it is necessary'.
A staggering 175,910 new cases were diagnosed yesterday, nearly treble the 65,000 cases on April 1.
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