Is the government pursuing herd immunity through mass infection?

More than 120 scientists have signed an open letter criticising Boris Johnson’s “dangerous and premature” plan to lift Covid restrictions on 19 July despite soaring infection rates.

The letter, published in The Lancet, says that “any strategy that tolerates high levels of infection” is “illogical”, since “vaccination offers the prospect of quickly reaching the same goal of population immunity”, also known as herd immunity, without the “grave risks”.

Urging the government to postpone so-called Freedom Day until more people have had Covid jabs, the scientists warn that the “dangerous and unethical experiment” could result in “a generation left with chronic health problems and disability”.

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Ministers have admitted that daily cases could reach 100,000 per day over the summer. But while the country is due to reopen before the national inoculation campaign is completed, they argue that vaccines have “broken the link” between infection and hospitalisations and deaths.

The prime minister’s official spokesperson insisted yesterday that “herd immunity is not in any way a government goal”.

Yet “it’s very much the virus’s”, writes The Times’ science editor Tom Whipple. Although each person with Covid-19 currently infects an average of 1.5 other people, he explains, “their subsequent hard-won immunity” becomes “another brick in the nation’s defences”.

And the government believes that the build-up of these defences will see Covid cases beginning to fall from August, sources told London Evening Standard. An insider reportedly said that Downing Street believes the virus will continue to “run through the unvaccinated and the single-dosed, but because such vast numbers of people now have antibodies and can resist it, it will then start falling off because it will run out of people to infect”.

According to the newspaper, Department of Health officials have coined a new term, “hybrid immunity”, to describe “the protection from vaccinating older, more vulnerable people, combined with a mixture of vaccinations and natural immunity in the young”.

Although No. 10 officially denies that herd immunity is a deliberate goal, “ministers say there is ‘an element’ of that in the situation being reached where a combination of natural immunity and herd immunity through vaccination will starve the virus of new hosts”, the Standard adds.

To date, 64.6% of UK adults are fully vaccinated, “although this drops to 50.7% when accounting for children”, reports Sky News.

But even as the jabs campaign continues, experts have noted the difficulties of pinpointing what percentage of the population needs to be immunised for the spread to stop.

In real life, “even small changes in transmission can have a big difference to the maths, because growth is exponential”, Dr Alexander Edwards, associate professor in biomedical technology at the University of Reading, told the i news site.

There is also “massive” local variation in behaviour and immunity, he added. And “thirdly, we have a mixture of natural infection, partial vs. full vaccination (one or two doses), and different vaccines - all of these give different levels of protection”.

The key question is “what is the public health cost” of reaching herd immunity, says Edwards, who argues that ”the more immunity comes from vaccination, the less likely to have harm from severe disease and long Covid arising from natural infection”.

Other experts have warned that reaching total herd immunity from Covid-19 may be impossible. Paul Hunter, professor in medicine at the University of East Anglia, points out that the AstraZeneca and Pfizer vaccines are slightly less effective against the Delta variant of Covid than against previous strains, and that immunity through vaccination and infection can wane over time.

For these reasons, the UK “will never reach herd immunity”, Hunter told i news. However, he added, Covid vaccines mean that “we do not need to”, as the jabs “substantially reduce the danger of getting severe disease on first infection”.