New figures show cases of the Indian variant of concern are growing fast, but from a low level.
The latest national figures show there are 1,313 cases of the variant of concern in the UK, up from the 520 recorded the previous week.
The cases are not evenly spread and are currently focussed in several areas where officials are especially concerned.
There are three types of the Indian COVID variant in the UK.
Public Health England (PHE) has designated one of them – B.1.617.2 – as a variant of concern. It is this that is increasing.
The other two Indian variants (B.1.617.1 and B.1.617.3) remain "variants under investigation".
The highest number of cases of the Indian variant of concern at the beginning of May were in Bolton, followed by Blackburn with Darwen, Leicester, Nottingham and Bedford, according to the Sanger Institute’s database.
The real number of cases of the Indian variant in these areas could be much higher. Sanger’s data shows only the number of samples of B.1.617.2 which have been found during genomic sequencing in laboratories.
The mayor of Greater Manchester, Andy Burnham, spoke of a "worrying" spike of cases among under 25s in Bolton and has asked for everyone over the age of 16 there to be offered a COVID-19 vaccine.
Prime Minister Boris Johnson has said he is "anxious" about the variant of concern, and a member of the Independent Sage group of experts has said the growth of the new variant leads her to conclude that next week’s planned relaxation of measures should be delayed.
But on Friday, vaccines minister Nadhim Zahawi insisted to Sky News that step three of England’s lockdown easing will still go ahead on Monday, despite the soaring cases of the Indian variant.
He said Monday’s plans would remain in place "because the vaccines are delivering" and "at the moment we have no evidence it [the variant] escapes vaccines".
Bolton has the second-highest current infection rate in the country, after Erewash.
Although the number of the absolute cases remain small, the growth rate is what worries the experts.
There is also concern about the growth of the Indian variant in Blackburn with Darwen which has the third-highest infection rate in the country. It has also seen the number of cases rise recently by 43%.
Across England, the number of cases of the Indian variant more than doubled in the week ending 12 May, from 520 to 1,313.
The European Medicines Agency has said it is "pretty confident" that current vaccines will be effective against the variant, an opinion that has been echoed by some British scientists.
Despite the increase in the Indian variant, data from Sanger still show the vast majority of the cases in the UK are the Kent variant which accelerated towards the end of last year.
It is also worth remembering that the overall number of confirmed cases in the UK has sharply decreased since the beginning of the year.
The growth of the Indian variant of concern led Prof Christina Pagel, a member of the Independent Sage group of experts, to argue that next week’s planned relaxation of measures should be pushed back.
In a series of tweets she warned that going ahead with the planned easing on Monday could "add fuel to the fire" of the Indian variant’s spread – and risks "more uncertainty, more damaging closures and longer recovery from a worse situation".
Analysis: Watching the data will continue to be crucial
By Ed Conway, Economics and data editor
Look beneath the UK headline data and you find something tentatively encouraging. In Bolton, among those aged under 60, the proportion of COVID cases (we’re talking here about overall cases, though we can probably assume a hefty chunk of these are the Indian variant) has more than trebled since late April – up from 54 per 100k on April 25 to 184 per 100k by May 7.
Now look at those aged over 60 – those, in other words, who are most likely to be vaccinated. Their levels of Covid have risen far less steeply, up from 29 per 100k to 43 per 100k. This is tentatively encouraging evidence that even if the Indian variant has established itself in Bolton, the vaccinated proportion of the population seems to have some protection.
In Blackburn with Darwen, another area where cases are rising (albeit less steeply than Bolton) and where the Indian variant has been detected, it’s a similar pattern: cases for those under 60 are rising faster than those under 60 (for whom COVID levels are broadly flat).
In short: there are certainly signs that this variant is spreading among the population. But, critically, there is also tentative real world evidence that the vaccines are working. It’s still too early to be sure of either of these conclusions, so watching the data in the coming weeks will be crucial.