The main issue around Covid boosters is encouraging people to take them up, rather than the timeframe between doses, a leading expert has said, as another called for the virus to be allowed to spread through the population.

Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), said the organisation would look at cutting the timeframe between second doses and boosters from six months to five, after Prime Minister Boris Johnson expressed interest in having a review.

However, Prof Harnden said six months had been shown to be the “sweet spot” for having a booster, saying the main issues in the programme were accessibility to the vaccine and persuading people to have one.

It comes as Paul Hunter, professor in medicine at the University of East Anglia, told the PA news agency the UK cannot reach herd immunity for coronavirus.

He said Covid-19 should be allowed to spread through the population once the most at-risk have been vaccinated “because that is how severe disease will be reduced in the long-term, and how the pandemic will ultimately become just another cause of the common cold”.

Coronavirus graphic
(PA Graphics)

Speaking on Times Radio, Prof Harnden said there was “some margin” around the six months between doses and it was possible to consider giving the booster earlier.

“I think it’s something that we will need to debate and consider, but I don’t think it’s the prime issue at the moment,” he said.

“The prime issue is to try and get those vulnerable, elderly people in particular, who would benefit from the booster, particularly when there are high infection rates and are more likely to get hospitalised and have serious effects from waning immunity, we need to get them in and get them boosted.

“So, there’s lots of work to be done in terms of accessibility. People can book an appointment by either phoning 119 or going on to the NHS website – so I think we just need to sort of whip up a bit more enthusiasm about the boosters amongst those vulnerable people.”

Elsewhere, on BBC Radio 4’s Today programme, Prof Harnden said shortening the timeframe would be looked at but added: “On JCVI, we’ve advised six months because that’s what the data shows is the sweet spot.”

Coronavirus graphic
(PA Graphics)

He said decisions on vaccinating the 40 to 50 age group did not need to be made yet, adding that those people eligible for the booster now would not have their second dose until April, “so it’s a long time before we need to consider the 40-year-olds.”

Asked whether restrictions may be needed, he said vaccines “can do the heavy lifting, but they can’t do everything, and actually we should still be maintaining social distances, we should be wearing masks in crowded spaces, and we should all remain sensible.”

Meanwhile, in an interview with the PA news agency, Prof Hunter said that herd immunity cannot be reached for coronaviruses and argued against continued social distancing.

Because protection against the infection is short-lived and wanes, the herd immunity threshold cannot be met, he suggested.

He added: “As the (Covid) infection is becoming endemic, pretty much everyone, whether vaccinated or not, will be getting repeated infections from now on, so any social distancing measures will not prevent infection, only delay it.

Coronavirus graphic
(PA Graphics)

“If someone is going to be vaccinated, then delaying infection till after vaccination has value, but if they are not going to be vaccinated then it does not.”

He said the value of social distancing to people not offered a jab or who will decline one “is pretty much zero”.

He added: “Professor Chris Whitty (chief medical officer for England) estimated that about 50% of schoolchildren have already had their first infection and I think he is correct.”

Prof Hunter said one caveat was that if health services become overwhelmed “then that is a threat to us all and that is a reason for further restrictions”.

However, he said, “most epidemiologists doubt we will see anything like last winter”.

Prof Hunter said he agreed with the president of the Royal College of Paediatrics and Child Health that routine testing in schools should be stopped.

“Like her I do believe what we are doing to children now is not necessary and damaging their education,” he said.

“Personally, I would argue that the role of vaccine was to reduce severity of disease during first exposure, but once we have vaccinated the most at-risk then we should let the virus spread because that is how severe disease will be reduced in the long-term, and how the pandemic will ultimately become just another cause of the common cold, as was the case the last time in (the pandemic of) 1890.”

Prof Hunter said he agreed that there were probably about 110,000 new infections per day in the country at the moment, once asymptomatic cases are taken into account.

It comes as Stephen Reicher, a member of the Sage subcommittee advising on behavioural science and professor of psychology at the University of St Andrews, told the BBC it was “simply wrong” to tell people they must go into work.

He said this was because “one of the key factors which determines the spread of the virus is how many contacts we have – if we have more contacts, we’re going to infect more people”.