UK Prime Minister Boris Johnson has cast doubt on the ability of Covid-19 vaccines to prevent a surge in cases as the country emerges from lockdown. He braced the public for an "inevitable" rise in cases as he said the three-month national shutdown in England had done "the bulk of the work" in reducing transmission of the virus to pre-September levels. The UK completed the first stage of its Covid-19 vaccine drive and will start offering the shot to younger people. All people aged 50 years and above and those from high-risk groups had been offered a first dose of a Covid-19 vaccine three days ahead of Thursday’s deadline. While vaccine uptake has been high among older people, scientists are concerned younger people who are at lower risk from Covid-19 might refuse. More than 32.2 million people have been given a first dose, with 7.7 million fully inoculated with a second. Mr Johnson said the UK remained on track to proceed to the next stage of the roadmap out of lockdown but warned the latest measures would lead to a rise in cases. "People, I don't think, appreciate that it's the lockdown that has been overwhelmingly important in delivering this improvement," he said. "Of course the vaccination programme has helped, but the bulk of work in reducing disease has been done by the lockdown. So, as we unlock, the result will inevitably be that we will see more infection, sadly we will see more hospitalisation and deaths. People have just got to understand that." Hailing a "hugely significant milestone" for the country, Mr Johnson said people aged 45 to 49 will be invited to receive an injection as the country proceeds to the next stage of its vaccine distribution strategy, which prioritises people based on their risk of serious illness from coronavirus. Mr Johnson said the programme had “already saved many thousands of lives”. “That means more than 32 million people have been given the precious protection vaccines provide against Covid-19,” he said. The success of the vaccine programme has underpinned Mr Johnson's roadmap out of lockdown. On Monday, all shops and outdoor hospitality venues reopened in England. The inoculation campaign took another step forward on Tuesday as the vaccine developed by Moderna started to be distributed in England – joining shots made by Pfizer-BioNTech and AstraZeneca-Oxford. Prof Adam Finn, from the University of Bristol, said the UK was “halfway up the hill” of inoculating all adults but he stressed the importance of younger people being vaccinated. “We’ve certainly got an important job to do to communicate the importance of the vaccination programme to younger people,” he told Sky News on Tuesday. “They perhaps have less fear of this disease than older people, but the ultimate exit from this catastrophe is building up immunity in the population. We need to get to the point that so many people are immune that the virus is left with nowhere to go.” Prof Finn, who sits on the government’s Joint Committee on Vaccination and Immunisation, said new variants of coronavirus were still risky. “We can’t now relax and assume the problem is finished,” he said. Prof Jeremy Brown from University College London said another wave of Covid-19 could lead to up to 50,000 deaths, even if most adults were inoculated against the disease. “I feel mighty relieved that we are now in a position where a very high proportion of the vulnerable population have been vaccinated so, if control of the virus is lost, then the damage it can do will be relatively restricted,” he said. “But when I say relatively restricted, what I mean is that a big third wave could still end up with 30,000 to 50,000 deaths, potentially, if it was a similar sort of size to the previous waves that we’ve had." Meanwhile, US infectious disease expert Anthony Fauci said he was optimistic about a “progression to normality” thanks to the distribution of vaccines. “Once you get people vaccinated, even though it may not be perfect, it will get the level of infection down to a dramatically lower level than it currently is,” he told the BBC. “Once you get a substantial proportion of the community vaccinated, you will have a greater level of control and be able to get back to some form of normality within a reasonable period of time. We’re very concerned about people who, for some reason or another, do not want to get vaccinated because that will allow this pandemic to continue.” 80+: 95.2% 75-79: 100% 70-74: 96.9% 65-69: 93.8% 60-64: 96.9% 55-59: 93.6% 50-54: 87.0%