The rapid spread of a more infectious Delta variant was laid bare today by a timelapse map revealing how it surged across the whole of England.
One of the Government's major Covid-tracking projects first spotted the subtype — dubbed AY.4.2 — in June, with 19 cases scattered across London and the South East. But within a week, the number of infections had doubled to 47, and the variant was advancing into areas of the Midlands, East of England and the South West.
And in just over three months it had reached almost every part of England. In the latest week more than 2,500 cases of the subtype were detected across the country, meaning it now makes up almost 10 per cent of all infections. The hotspot is in Adur, West Sussex.
Scientists say the subtype — thought to be 10 to 15 per cent more transmissible than Delta — likely first emerged in the UK because of the high number of infections here compared to other countries, which gives the virus more chances to mutate.
A separate dataset tracking variants globally puts its first emergence in Britain at June 14, followed by Ireland in late June, Germany in July, and Denmark and the US in August.
There is no evidence that it makes vaccines less effective or is more likely to trigger hospitalisation and death, but No10 has vowed to keep a 'close eye' on AY.4.2.
It has been suggested that the World Health Organization will elevate the subtype to 'Variant under Investigation' in the coming days. It is likely to be named 'Nu', the next letter in the Greek alphabet.
But experts today insisted there was no reason to panic, adding this subtype did not represent the same change as when Delta replaced Alpha.
The warning comes as Covid cases continue to spiral across the UK, with daily infections yesterday shooting up to almost 50,000 in a three-month high.
Experts suggested the uptick of AY.4.2 may be partly to blame, along with the return of pupils to classrooms from August and workers to offices.
There have been some 20,248 cases of AY.4.2 in the UK to date, data suggests, and 13 in the US.
The above maps show the proportion of Covid cases that were the Delta sub-variant AY.4.2 in the fortnight to June 26 (left) and the fortnight to July 31 (right). Darker colours indicate that more cases of the sub-variant had been detected
The above maps show the proportion of cases that were AY.4.2 in the fortnight to September 25 (left) and October 9 (right). The darker colours indicate that a higher proportion of infections were down to this sub-variant.
The above graph shows Covid cases per million people in the countries that have detected AY.4.2. It was first spotted in the UK on June 26, before being detected in Germany on July 5, Denmark on August 2 and the US on August 16. Experts have suggested that AY.4.2 likely evolved in the UK because the country has a higher case rate than others. Although the US had a similar infection rate in August, it did not spot the variant until almost two months after the UK did
The above graph compares the number of Delta cases with mutations seen on AY.4.2 spotted in the UK and other countries reporting more than ten cases of the variant. It also includes the US where four cases have been detected. It shows the variant was first picked up in the UK on June 14, and then detected in Ireland on June 28
There have been suggestions that the variant may be elevated to 'Variant under Investigation'. If this is the case the World Health Organization is likely to give it the name 'Nu', which is the next letter in the Greek alphabet
Scientists are monitoring Covid infections to track the spread and emergence of variants, in case one mutant strain that is more infectious or better able to evade vaccine-triggered immunity appears.