The idea of defeating Covid-19 by reaching herd immunity through mass vaccination is “mythical” because the Delta variant means it will be impossible to eliminate coronavirus, the head of the UK’s vaccines watchdog has said.

Andrew Pollard, chair of the Joint Committee on Vaccination and Immunisation (JCVI), suggested to MPs that giving jabs to children would not help stop the spread of Covid-19 among those people who are most likely to fall seriously ill.

His committee recommended last week that all Britons aged 16 and 17 should be offered at least one dose of the Pfizer vaccine, and is currently considering whether younger teenagers should also be given the opportunity to get vaccinated.

Speaking to the all-party parliamentary group on coronavirus, Sir Andrew insisted Covid-19 should not be compared to measles which is controlled through a universal vaccination programme ensuring it cannot spread through the population. He said: “What we know very clearly with the coronavirus that this current variant, the Delta variant, will still infect people who have been vaccinated and that means that anyone who is unvaccinated will meet the virus.”

Sir Andrew said that vaccinated people who contract Covid-19 did appear to be less infectious, but added: “I think we are in a situation here with this current variant where herd immunity is not a possiblity because it still infects vaccinated individuals.” He suggested that would undermine the argument for vaccinating children, which has been partly based on the idea that protecting children would stop them spreading the virus to vulnerable adults, and called for the Government to focus on giving vaccines to as many adults as possible so they do not end up in hospital if they are infected.