THE R rate in parts of England is as high as 2.5 due to the Delta variant first seen in India, “Prof Lockdown” has warned.

Prof Neil Ferguson, whose modelling scared the Government into the first lockdown, said the best guess is Delta is 60 per cent more transmissible.

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That’s compared to the Alpha (Kent) variant which is no longer dominant due to the new, rapidly spreading Delta strain.

Prof Ferguson, Director of the MRC Centre for Global Infectious Disease Analysis, Imperial College London, said cases of the Delta variant were doubling within less than a week.

He also revealed ministers were warned last week of a “substantial third wave” in the UK.

The updated modells from scientists reporting to Sage – the Government scientific advisory group – are bound to be considered as the PM decides whether to go ahead with the June 21 unlocking.

Prof Ferguson told journalists in a virtual briefing: “I think I said last week we have evidence the Delta had something between a 30 and 100 per cent transmission advantage over the Alpha variant. 

“That’s firmed up. We think 60 per cent is about the best estimate, but ranging between 40 and 80 per cent advantage. 

“And what I mean by that is the R number for Delta is about 40 to 80 per cent higher than Alpha. 

“There is a lot of regional variability. But on average, R for Delta across different authorities in the country is ranging from about 1.2 to 2.5, and 1.5 being the average.”

Speaking of the new worrying models of what could happen over summer, Prof Ferguson said: “Basically it's saying there is a risk of a substantial third wave. We cannot be definitive about the scale of that.

“It could be substantially lower than the second wave or of a similar magnitude.”

Modelling given to Sage by scientists in May suggested that even with vaccines, a variant that is 50 per cent more transmissible could see daily hospital admissions reach 5,500 without June 21 "Freedom Day" going ahead.

This compares with 3,000 at the peak of the first wave (April 2020), and 4,000 in the second (January 2021).

The forecasts were made before new data showed the Delta variant can also weaken the efficacy of vaccines.

Prof Ferguson said the models have been “improved and refined” but there is “still a lot of uncertainty” because there are unknowns about how Delta will spread as people socially mix more.

The significance of another wave “critically depends on how effective the vaccines still are at protecting people against hospitalisation and death against the Delta variant”, Prof Ferguson said.

“One of the key things we want to resolve in the next few weeks is do we see an uptick in hospitalisations –  we are seeing it in some areas, but a consistent uptick and growth in hospitalisations matching cases.”

Prof Ferguson said as time passes, however, hospitalisations will inevitably go upwards. 

He said: “In the last few weeks it's been much more of a picture of hotspots – Bolton, Bedford and others – and a quite noisy picture elsewhere. 

“Now we are seeing a much clearer picture of exponential growth of Delta in the large majority of local areas. But still in many of those areas it's at quite low levels.

“As time pases, the numbers will get larger and we’ll start getting more of a signal in hospilatiosn as well, for the same reason – just larger numbers.”

The official R rate given by Sage for England is between 1 and 1.2, reaching 1.0 to 1.3 in the North West.

Prof Ferguson did not reveal what local areas the R rate was 2.5.

Delta variant hotspots have mostly been in the North West, with Bolton and Blackburn with Darwen seeing the highest infection rates for several weeks.

Bedford and Manchester have also been seeing spikes in cases recently. 

The R rate represents how many people an person infected with Covid spreads the virus on to.

The coronavirus has a natural R which can be lowered by restrictions that limit social contact.

It’s ideal to keep the value below 1, because that means the outbreak is shrinking.

Prof Ferguson suggested the natural R rate of the Delta variant is several times higher than that of the original coronavirus from Wuhan, China.

It looks to be between 5 and 8 against the Wuhan strain’s 2.5, and Alpha’s 4-5. But Prof Ferguson added “the uncertainty is quite large”.

Asked whether the England should delay the final stage of lifting Covid restrictions, Prof Ferguson said: "Clearly you need to be cautious if you want measures to be irreversibly changed and relaxed."

Prof Wendy Barclay, lead of G2P-UK which studies the threat of new variants told the briefing: "The vaccine has to work that little bit harder to protect us all against Delta, and therefore it’s even more so important to get second doses and raise that immune response.

"Any delays, talking from a purely scientific basis, will help because they will allow more time or people to get the second doses.

"Having a second dose itself is not enough. You need around seven days after the second dose for the vaccine to really boost the immune response back up to levels you'd like it to be."

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