Boris Johnson has said there is still “nothing in the data at the moment that means we cannot go ahead with step 4” of lifting coronavirus restrictions in England on June 21.
But the prime minister added the people needed “to be so cautious” as infection rates were increasing.
He said on Wednesday the public would have to “wait a little bit longer” before the government would announce for certain what would happen on June 21.
On June 14 ministers are due to meet and review data relating to Covid and the spread of the Delta variant, previously known as the Indian variant.
Johnson added: “What we need to work out is to what extent the vaccination programme has protected enough of us, particularly the elderly and vulnerable, against a new surge, and there I’m afraid the data is still ambiguous.”
Experts are split over whether the final stage of lifting coronavirus restrictions should go ahead amid fears over a potential third wave of the pandemic.
Professor Adam Finn, of the Joint Committee on Vaccination and Immunisation (JCVI), said there are still many people who are vulnerable to the effects of Covid, as he warned that pressing ahead with the easing of restrictions on June 21 “may be a bad decision”.
Sir John Bell, regius professor of medicine at Oxford University, told BBC Radio 4’s Today programme that current figures “don’t look too intimidating”.
He said they still need to “play out for a couple of weeks” before the government makes its final decision.
The government’s former chief scientific adviser, Sir Mark Walport, has also argued that ministers need more data before they can make a final decision.
But Robert Dingwall, professor of sociology at Nottingham Trent University, has gone further, arguing it is “really important that we go ahead on June 21” from a “societal point of view”.
Following the recording of zero Covid deaths on Tuesday, health secretary Matt Hancock said “vaccines are clearly working”.