Cases of the Delta variant of Covid-19 first identified in India have risen 46% in a week across the UK, new figures show.
Public Health England said there had been 35,204 more cases since last week to reach a total of 111,157 - a 46% increase.
Some 42 of these cases are the Delta AY.1 sub lineage.
India's health ministry has said studies show that this so-called Delta plus variant spreads more easily, binds more easily to lung cells and is potentially resistant to monoclonal antibody therapy, which can help neutralise the virus.
But while the Delta variant now accounts for around 95% of new cases sequenced in the UK, PHE said vaccines continue to have a "crucial effect on hospital admission and death".
A further 514 people were admitted to hospital in England with Covid-19 in the week up to 21 June. Of these, 304 were unvaccinated.
Dr Jenny Harries, chief executive of the UK Health Security Agency, said: "Through the success of our vaccination programme, data suggest we have begun to break the link between cases and hospitalisations. This is hugely encouraging news, but we cannot become complacent.
"Two doses of vaccine are far more effective against Covid-19 than a single dose, so please make sure that you come forward to get your second dose as soon as you are invited.
"Whilst vaccines provide excellent protection, they do not provide total protection, so it is still as important as ever that we continue to exercise caution.
"Protect yourself and the people around you by working from home where possible, and by practising 'hands, face, space, fresh air' at all times."
PHE also said a further variant, Lambda (C.37), has been designated as a variant under investigation (VUI) due to a rise in international cases and several notable mutations.
Six cases of Lambda have been identified in the UK to date, all of which have been linked to overseas travel.
PHE said tests were ongoing and there is currently no evidence that this variant causes more severe disease or renders vaccines less effective.
The body also said the figures for variants this week are likely to be an underestimate owing to an operational issue being investigated by the Wellcome Sanger Institute on potential cross-contamination of a number of positive Covid-19 samples.
PHE said these samples were PCR tested before they were sent to the Sanger Institute, meaning people have received their correct test result and positive cases told to isolate.