n 17 September the government’s scientific advisory group, Sage, met. Its minutes note that a national “circuit breaker” lockdown for England “could have a significant impact on transmission”, stating that the “approach has greater impact when the epidemic is growing faster”. A second wave had been all but inevitable after the lifting of national restrictions on 4 July, the introduction of the “eat out to help out” scheme, and the easing of travel restrictions and quarantining, which allowed people to take holidays to Covid-transmission hotspots such as Spain. On 21 September, Prof Chris Whitty and Prof Sir Patrick Vallance held a public briefing where they presented worst-case scenario figures for Covid cases and deaths into autumn and winter if no action was taken. The briefing was widely criticised as scaremongering, but the projected figures of 50,000 cases and 200 deaths per day has proved to be largely correct, with 45,000 cases and 450 deaths per day in October-November. The same day, Sage set out in an official document that a circuit breaker “should be considered for immediate introduction”. A report in the Sunday Times over the weekend suggests that the decision not to impose a circuit-breaker lockdown was influenced by a meeting involving the prime minister, the chancellor and three proponents of a “herd immunity” approach to managing the virus: Prof Sunetra Gupta and Prof Carl Heneghan of the University of Oxford and Prof Anders Tegnell, the Swedish epidemiologist who has masterminded Sweden’s catastrophic Covid control policy (in the last month, Sweden has reported 1,400 Covid deaths, while neighbours Norway and Finland, both of which have roughly half its population, reported 100 and 80 respectively). The delay in imposing national restrictions resulted in an estimated 1.3 million extra Covid infections. The idea behind the “herd immunity approach” is that we should allow Covid to run through the majority of the population, who will supposedly have very minor symptoms, while shielding our most vulnerable members of society. The belief is that this would generate immunity to the extent that the virus would have insufficient hosts to infect, and would die out. The problem with this hypothesis is that is completely scientifically flawed, and there is no data to support it. And yet it continues to be pushed. In March, Gupta and colleagues raised the possibility that half of the UK population had already been infected by Sars-CoV-2. This was subsequently shown to be false. In September she stated that the worst-case scenario presented by Whitty and Vallance, of 50,000 cases per day, was very likely wrong – but it has been proved largely right. First, we don’t have sufficient evidence regarding the extent of natural protective immunity after Sars-CoV-2 infection. Indeed, we know that re-infection is possible. Second, Sars-CoV-2 doesn’t just infect humans – it has been documented in mink and family pets. This means that even if the human population did become immune, those shielded would still be at risk as the virus could be maintained in animal hosts. Thirdly it is naive in the extreme to suggest the young and healthy will not suffer serious symptoms from Covid infection, with deaths occurring in all age groups and a number of post-infection complications well documented. And finally, no mechanism by which we could effectively shield all vulnerable members of society has been demonstrated. The idea of preventing large swathes of the country from being exposed to Covid is near ridiculous, as evidenced by the situation in care homes across the country. Herd immunity is only an effective strategy for infectious diseases when it’s achieved via vaccination, not by natural infection. A study of the Brazilian city of Manaus suggested that, left to spread unchecked, Covid can infect up to 75% of the population with devastating consequences. In short there is no “safe” way to allow Covid to run through a population without upending the healthcare system and experiencing an unacceptable number of fatalities. This is not just my opinion, it is the mainstream view of every respected infectious disease researcher in the country (and across the world, as evidenced by the John Snow memorandum). That such a fringe view could be presented to the prime minister as he weighed a decision on national Covid containment policy is deeply disturbing, especially when it flies in the face of the opinion of the government’s most respected scientific advisers. More disturbing still is that our government appears to make important decisions on Covid based on the economy, repeating the same mistakes while failing to grasp that the only way to protect prosperity is to suppress Covid as far as possible until widespread vaccination has occurred. • Alan McNally is a professor in microbial genomics at the University of Birmingham