The Covid variant first identified in India could be 60% more transmissible than the strain that spread rapidly through the UK in the winter, a former Government adviser has said.
Professor Neil Ferguson, one of the architect’s of the first lockdown, said the Delta strain could be between 30% and 100% more infectious than the previously dominant Kent variant – now known as Alpha.
And he warned that the best estimate was it was 60% more transmissible – a higher figure than experts have so far suggested.
His comments will spark further concern over whether the UK can proceed with the final step of the lockdown roadmap on June 21.
It will also ramp up pressure on the Government over why India was not added to the red list of countries sooner.
Public Health England said on Thursday that the Indian strain was now the dominant variant in the UK – with cases rocketing by 5,472 since last week to 12,431.
Boris Johnson is waiting for critical data on how easily the Delta strain spreads before he makes a decision on whether to press ahead with the June 21 lockdown lifting.
The Prime Minister has insisted that there is nothing in the data to suggest so-called Freedom Day needs to be delayed – but he has struck a more cautious tone in recent days.
It also comes after the Government axed quarantine-free travel to Portugal amid fears over the prevalence of the variant in the country.
Prof Ferguson told Today: “Unfortunately, I mean, the news is not as positive as I would like on any respect about the Delta variant.
“The best estimate at the moment is this variant may be 60% more transmissible than the Alpha variant.
“There’s some uncertainty around that depending on assumption and how you analyse the data, between about 30% and maybe even up to 100% more transmissible.”
Prof Ferguson said 60% is “a good central estimate” at the moment.
SAGE papers recently revealed that experts feared it was up to 50% more transmissible but Deputy Chief Medical Officer Jonathan Van Tam said it was likely to be half that.
The Imperial College expert warned that the data was “pointing this week in a more negative direction than it was last week”.
Asked if lockdown lifting could go ahead, he told the Today Programme: “First of all, it’s not my job to make that decision, thankfully.
“I think the data is pointing this week in a more negative direction than it was last week, so it points towards the direction of being cautious.
“I think balancing, clearly, people’s desire – and there clearly is a built-up desire to get back to normal – against the potential risk is a very difficult judgment call.”
Asked whether a delay would make a difference, he said: “We know at the moment that the Delta variant, the Indian variant, is doubling across the country about every nine days with some variability place to place.
“But we haven’t fully seen the effect of what happened May 17 step three, the relaxation of restrictions, come through into that data, so we expect that to accelerate even more.”
Cabinet Minister Robert Jenrick maintained there was still “nothing at the moment that suggests that we won’t be able to move forward” with the next stage of lifting restrictions on June 21.
He told Today: “We’ve got a further 10 days until we are going to make that decision on or around June 14, so during that period we’ll see where are we with hospitalisations, with deaths, where are we with the vaccine rollout – we’re doing everything we possibly can to expedite that – and then at that point, we’ll make our final decision.”