Professor Adam Finn, of the Joint Committee on Vaccination and Immunisation (JCVI), said on Tuesday that pressing ahead with the lifting of final restrictions on 21 June “may be a bad decision”.
The adviser said many people remain vulnerable to the effects of Covid-19 despite the success of the vaccine roll-out.
“There’s vulnerability across the country – the idea that somehow the job is done is wrong,” Prof Finn told BBC Radio 4’s Today programme.
"We’ve still got a lot of people out there who’ve neither had this virus ... nor yet been immunised, and that’s why we’re in a vulnerable position right now.”
Professor Ravi Gupta, a member of the government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said on Tuesday that pushing back the end of lockdown would be wise.
“We need at least a few weeks, probably a month,” Prof Gupta told Sky News – arguing that 21 June would be “too soon” to end social distancing curbs.
The adviser said it could made clear to the public that any delay would only be a temporary measure based on the surge of the Indian variant.
Dr Chaand Nagpaul, the British Medical Association’s council chair, has urged the prime minister to be guided by the data rather than fixed dates – warning him not to “repeat” the past mistakes of 2020.
However, other experts believe there is no reason to push back the final stage of the roadmap, which would see nightclubs reopen and social distancing dropped inside pubs and restaurants.
Robert Dingwall, professor of sociology at Nottingham Trent University, said it was important to press ahead with the 21 June easing.
He told Times Radio: “I personally don’t see any case for delay ... from a societal point of view, I think it’s really important that we go ahead on June 21 and I’ve not really seen anything in the data that would lead me to doubt that.”
Prof Dingwall said: “We’ve got to think about the impact of economic damage that would be caused by further periods of delay and uncertainty.”
He added: “By the time we get to 21 June, everybody who is in the nine priority groups or the highest risk will have had both jabs and would have had a period of time to consolidate the immunity.
“What are we going on with is really running into younger age groups who are intrinsically much lower risk. Many of the scientists … simply haven’t adjusted their expectations to understand that [for these people] Covid is a mild illness in the community.”
The race to vaccinate has gathered pace after a major walk-in centre at Twickenham Stadium opened up the jab offer to over-18s. Currently, only those aged over 30 in England are being invited to book their first vaccine
Just over 39 million people in the UK have been given a first dose, and a further 25 million have had both does.
It means almost three-quarters (74.8%) of the adult population has had their first Covid jab, with almost half (48.5%) having had their second.
The government’s former chief scientific adviser Professor Sir Mark Walport told said ministers still needed more data before they can make a final decision on lockdown lifting.
Sir Mark told BBC Breakfast: “We need to substitute speculation for scientific data that’s the truth of the matter.”
He said the government had to know more about the transmissibility of the data and the impact in changes in behaviour following the big relaxation of measures on 17 June.
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