A Claim of Herd Immunity Reignites Debate Over U.K. Covid Policy


LONDON – In the four months since Prime Minister Boris Johnson took the risk of lifting virtually all of England’s coronavirus restrictions, his country has entered an alarming new normal, with more than 40,000 new infections per day and close to 1,000 deaths each week.

However, these bleak numbers have put the UK “near herd immunity”, as one of the government’s most influential scientific advisers said this week, is a widely discussed but elusive epidemiological condition that some experts say could leave the country. in good conditions to withstand the new wave of infections now sweeping continental Europe.

Comments made in an interview by Neil Ferguson, an epidemiologist at Imperial College London, whose pandemic predictions have often influenced government policy, are likely to revitalize the debate about the UK’s status as an exceptional Covid country: a country willing to tolerate a widespread virus and constant death tolls like the cost of returning to normal economic life.

They can also hurt a nerve in a country where herd immunity was a dangerous concept. as it was raised by Patrick Vallance, England’s chief scientific advisor, in March 2020. since the virus first attacked the UK. His openness to the benefits of herd immunity prompted such reactions that the government has since rejected any suggestion that it supported such a strategy.

Speaking to a group of international reporters on Tuesday, Professor Ferguson said he expects the UK to largely avoid the spike in cases seen across the continent in recent weeks. In part, this happened, he said, because so many Britons had been infected since the isolation was lifted in July, giving the population as a whole better immunity.

“We may well see a few weeks of slow growth, but in some ways we are almost at herd immunity,” he said, adding that the UK is in a slightly better position than countries like Austria, the Netherlands and Germany, where restrictions reintroduced in conditions of rapidly increasing infection rates.

Other public health experts are skeptical of Professor Ferguson’s theory, not least because the high infection rate in the UK suggests there are still large numbers of people with low or no immunity. They say he also doesn’t take into account other factors, such as new options or weakening vaccine defenses.

“This is a bold statement,” said Devi Sridhar, head of the global public health program at the University of Edinburgh. “I don’t think the modelers have enough data to assess whether we have reached the mythical stage of herd immunity. With Covid, this will happen either when everyone has been ill with Covid and survived, died from it, or were vaccinated against it. “

According to the Mayo Clinic, herd immunity occurs “when a large portion of the community (herd) becomes immune to disease, making it unlikely that the disease will spread from person to person. As a result, the whole community is protected, not just those who do not have immunity. “

Professor Sridhar said that given the rapid spread of the Delta variant, it is possible that Britain will reach that threshold after winter. But that will depend on the resistance of the vaccines and natural immunity. Meanwhile, she said she was worried about hospital capacity from December to February, when colder weather could trigger infections like Covid-19 and seasonal flu.

Despite repeated government denials that it is pursuing a herd immunity strategy, suspicions persist, especially after Mr. Johnson lifted all restrictions in England on July 19, prompting the London press to declare it a “freedom day.” Scotland, Wales and Northern Ireland left some restrictions at the time.

At the time, health officials said it would be better to see a potential spike in infections in the summer months than in winter, when the virus tends to spread more easily and when there is a peak hospital load.

Among the scientists who became familiar figures during the pandemic, Professor Ferguson stands out. In March 2020, his modeling team warned that an uncontrolled spread of the disease could cause up to 510,000 deaths in the UK and up to 2.2 million in the United States – alarming projections that have prompted both to accelerate their transition to isolation. (There were 144,137 deaths in the UK and 774,580 in the US).

In May 2020, Professor Ferguson, nicknamed “The Professor of Isolation” by the British tabloid press, briefly resigned as a government adviser after admitting a violation of isolation rules by accepting a woman in his home. But his views continued to carry weight, and he again became a member of the government influential Scientific Advisory Group on Emergencies, or SAGE.

This time, Professor Ferguson has a more encouraging message: The increased levels of immunity in the UK means there is no need for further restrictions at this time, even if the number of cases increases slightly.

Professor Ferguson said the decision to lift the restrictions in England was motivated by the determination of politicians to return to normal life, rather than bolster immunity by allowing the virus to spread among the population.

But to some extent, the difference is no difference: the number of cases reported in the UK since July is five million, more than half of the total since the start of the pandemic. That’s the equivalent of 7.5 percent of the population, Professor Ferguson said, and that figure could probably double if added to those without symptoms.

This rapid circulation of Covid boosts immunity in unvaccinated young people and adolescents, as well as in vaccinated people, he says – essentially “replenishing” their immunity, he said. Combined with the effective introduction of vaccines and boosters in the UK – about 80 percent of the population received at least two doses – a high level of immunity allows maintaining a relatively stable number of cases, albeit at a high level.

Of course, he added, the British approach “was not free.” The country’s daily death toll still exceeds that of its neighbors.

“Herd immunity is not an all-or-nothing principle,” said Professor Ferguson. “This is what limits transmission, and having a mostly flat transmission where we have no real restrictions in England, suggests that we are almost on the cusp of an immunity that will stop transmission.”

However, there are still too many wild cards for skeptics to conclude that the UK pandemic is fizzling out.

“We really don’t understand Covid and many of its newer variants,” said Tim Spector, professor of genetic epidemiology at King’s College London, who led the Zoe Covid Study, which tracks the symptoms of Covid-19.

According to Professor Spector, previous predictions about herd immunity have turned out to be wrong, and assumptions about the background of its occurrence continue to be revised. In 2020, scientists said a country could achieve herd immunity if approximately 60 percent of its population were immune. More recently, scientists revised the estimate to 85 percent or higher – and some argue that in the US at least it may never be achieved.

Epidemiological models also do not account for decreased immunity. “The vaccines are partly working,” said Professor Spector. “But they also wear off to varying degrees in different people. With weakening immunity, this battle will probably never be completely won. “

This is more than academic arguments. The discussion of herd immunity is turning into “a general government strategy that paints a rosy picture,” he said. “You hear government ministers say 40,000 cases a day is a success story.”

Behind the herd immunity debate lies a more fundamental question of whether the government was right in opening up England’s economy and society last summer, even when the virus was still circulating widely among the population.

“We act as if Europe is much worse, but we just put up with the higher death toll and higher infection rates for a longer period,” said Professor Sridhar.


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