Scientists have warned the government that waiting for definitive proof the Indian variant is more transmissible could mean any action to halt the spread might be too little, too late.
The Scientific Advisory Group for Emergencies (SAGE) published a document on Friday urging "rapid containment" in areas affected by the B.1.617.2 variant that is believed to have originated in India.
The briefing note states: "Incontrovertible evidence that B.1.617.2 is more transmissible may come too late.
"In the face of uncertain evidence the risk of over-reacting seems small compared to the potential benefit of delaying a third wave until more people are vaccinated.
"Rapid containment in Bolton and Blackburn, Sefton, Liverpool, and the area around Bedford is warranted.
"Surge testing for B.1.617.2 in these areas is needed."
The document goes on to recommend "active surveillance for further outbreaks" and "aggressive use of asymptomatic testing and contact tracing" in targeted areas to contain or delay outbreaks.
It says that surge vaccinations - a strategy that some local leaders have called for is "worth considering" but may not be sufficient on to prevent any outbreaks because because protection will take time to develop.
"Surge vaccination will redistribute vaccines, and require increased local resources, may not be achievable if growth continues," it adds.
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On Friday afternoon Boris Johnson's official spokesman said that the Prime Minister was "monitoring" the spread of the Indian variant as well as a new strain of coronavirus identified in Yorkshire labelled a "triple mutant" strain.
The PM consistently reiterated that the 21 June target date for lifting more restrictions remains on track for now.
Some experts were quick to highlight the recommendations of the Sage report, including ramping up testing and surge vaccinations, and urged caution ahead of the next step in lifting lockdown.
Dr Zubaida Haque, a founding member of Independent Sage - a body unaffiliated to government that aims to provide advice regarding COVID - wrote on Twitter that the "key point which sticks out" in the document is that "In the face of uncertain evidence the risk of over-reacting seems small compared to the potential benefit of delaying a third wave until more people are vaccinated".
"We are *1 month away* from next step of roadmap," she wrote.
And Professor Christina Pagel, a professor of operational research at University College London said: "They urge caution!" while highlighting the text recommending stepped-up surveillance.
However, despite the concern surrounding the spread of the Indian variant, Boris Johnson has insisted that England is on course to continue its 'roadmap' out of lockdown.
But, he added: “We’ve got to be cautious and we are keeping everything under very close observation.
“We’ll know a lot more in a few days’ time.”
On Friday, the Office for National Statistics said the number of people testing positive for coronavirus in England is showing “early signs of a potential increase".
Around one in 1,110 people in private households in England had COVID-19 in the week to 15 May – up from one in 1,340 the previous week.
However, Sarah Crofts, Head of Analytical Outputs for the COVID Infection Survey, said the rates were too low to say whether this was the start of a new trend.
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