A leading vaccine scientist is “optimistic” the UK will achieve herd immunity against Covid-19 despite the spread of the Indian variant. Prof Adam Finn, a paediatrician and government vaccine adviser, said on Thursday the country could still beat the disease if uptake of the vaccine remained high. "We're now confronted with, yet again, another version of the virus and we're still in the process of understanding how infectious it is," he told BBC's Radio 4 <em>Today</em> programme. "The proportion of the population and the evenness with which you give them the vaccine ultimately will determine when you achieve population immunity for any infection. I'm optimistic that we, particularly in the UK, with the high coverage we're achieving and the extremely effective vaccines we've got, that we can achieve population immunity." Prime Minister Boris Johnson is also increasingly confident that the final stage of lockdown easing will take place on June 21. He said there was "nothing conclusive" in the data that means England "would have to deviate from the roadmap". "We have increasing confidence that vaccines are effective against all variants, including the Indian variant." The number of confirmed cases of the India variant rose to 2,967 on Wednesday – up 28 per cent from Monday’s 2,323. However, England’s deputy chief medical officer Jonathan Van-Tam said hospital admissions remained “fairly flat” in variant hotspots. He said the India variant could be between 20 and 30 per cent more infectious than the strain first identified in England, but vaccines would guard against serious illness. “I pitch this personally as a straight race between the transmissibility of this new variant … and vaccine delivery,” he said. “The NHS is doing everything it can to turbo-boost that, and that is the challenge that’s ahead of us in the next two to three to four weeks, to make sure that we outrun the virus through really vigorous pull-through on vaccine delivery.” The UK opened its vaccination programme to those aged 34 and above on Wednesday. More than 70 per cent of the adult population has received the first dose, and nearly 40 per cent are fully vaccinated, government data shows.