A leading British immunologist says governments should not overreact to new strains of Covid-19 if a significant proportion of their population is vaccinated against the disease. Prof John Bell, an adviser to the UK government, said people should not “scamper down a rabbit hole every time we see a new variant”, because Covid-19 would circulate, “probably for ever”. He said he was not unduly concerned by the UK's recent increase in case numbers fuelled by the Delta variant first seen in India, because hospital admissions were still low. Britain on Tuesday recorded <a href="https://www.thenationalnews.com/world/europe/uk-records-zero-daily-covid-deaths-for-first-time-since-march-2020-1.1233754">no Covid deaths for the first time since the pandemic began</a> in March last year. "I am pretty encouraged by what I see," Prof Bell told the <em>Today</em> programme on BBC Radio 4 on Wednesday. “We do need to keep our eye on hospitalisations, serious disease and deaths, which is really what we’re trying to manage," he said. "If we scamper down a rabbit hole every time we see a new variant we’re going to spend a long time huddled away. We need to get a bit of balance in the discussion and keep our eye on the serious disease we’re trying to prevent.” He said it was vital to get more young people vaccinated. “This disease is here to stay, probably for ever, but that’s one of the reasons why we need to move on and try to suppress the disease as much as possible around the world, otherwise we’re going to sit here and get slammed by repeated variants as they come through the door,” he said. Prime Minister Boris Johnson said on Wednesday the UK remained on track to lift the last remaining social distancing restrictions on June 21. However, he stopped short of promising to do so as he still needs more information to inform his decision. "I can see nothing in the data at the moment that means we can't go ahead with step four, or the opening up on June 21, but we've got to be so cautious," he said. "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 just still ambiguous. “The best the scientists can say at the moment is we just need to give it a little bit longer." On Wednesday the UK hit the milestone of having administered a first dose of Covid-19 vaccine to three quarters of adults. UK government data shows that more than 39.4 million people have received a first dose – 74.9 per cent of those aged over 18. Health Secretary Matt Hancock was expected to praise the work of scientists for developing a coronavirus vaccine in less than a year when he addressed a G7 meeting in London this week. “The biggest risk would have been the failure to find a vaccine at all. We explicitly embraced risk early on, so we backed lots of horses and invested at risk,” he was expected to say. “And instead of sitting back and waiting to see which vaccines came off, we were tenacious in helping them to get over the line, drawing on the abundant industry experience in our team.” Mr Hancock said on Tuesday that "vaccines are clearly working" but that Britain had not "beaten this virus yet". However, it is hoped that, despite the spread of the Delta variant, vaccines will break the link between infection, hospital admissions and deaths. The latest daily figure for admissions was 133, compared with a high of 4,500 in the winter. The number of people on ventilators in intensive care was 120 – down from 4,000 at its peak. On Tuesday, 3,165 new infections were confirmed in the UK – the seventh consecutive day that the figure topped 3,000. The majority of new cases were said to be in people under 50, who had not received both doses. Some scientists said that a third wave was taking hold and Scottish First Minister Nicola Sturgeon <a href="https://www.thenationalnews.com/world/europe/scotland-puts-the-brakes-on-road-map-out-of-lockdown-1.1233609">delayed the country's road map out of lockdown</a>. She said a "slight slowing down" of unlocking was needed while vaccines are distributed. "The vaccines make the outlook positive, but the new variant means the road ahead is still potentially bumpy, so caution is necessary,” she said. Several scientists, many of whom are advising the UK government, <a href="https://www.thenationalnews.com/world/europe/disney-like-queues-at-twickenham-rugby-stadium-as-over-18s-are-offered-vaccines-1.1233090">urged Mr Johnson to take a similar approach</a> and postpone the <a href="https://www.thenationalnews.com/world/europe/when-can-i-travel-again-uk-roadmap-s-four-stages-explained-1.1171301">last step of reopening for England</a>. Prof Adam Finn from the University of Bristol said many people were still vulnerable to Covid-19 – a warning to the public that "the idea that somehow the job is done is wrong". “We've still got a lot of people out there who have neither had this virus infection nor been immunised and that's why we're in a vulnerable position right now,” he said. Prof Ravi Gupta from the University of Cambridge said a delay of a few weeks could have a significant effect on Britain’s battle against the pandemic. “We really should be making sure we think about what we're doing in the context of this new, unknown virus,” he said. Pat Cullen, acting general secretary and chief executive of the Royal College of Nursing, urged ministers to pay close attention to hospital admissions. "As the NHS starts the road to recovery, now is the time to take cautious steps and not take an unchecked leap to freedom," she said.