Herd immunity for COVID-19.

In early October, 2020, three epidemiologists convened in Great Barrington, a small town in Massachusetts, USA. Jay Bhattacharya (Stanford University Medical School, Stanford, CA, USA), Sunetra Gupta (University of Oxford University, Oxford, UK) and Martin Kulldorff (Harvard University, Cambridge, MA, USA) were there to draft an argument for a new strategy to combat COVID-19. They called it the Great Barrington Declaration. It has since been endorsed by thousands of medical practitioners, researchers, and public health scientists.

“Current lockdown policies are producing devastating effects on short and long-term public health”, states the declaration. “Keeping the measures in place until a vaccine is available will cause irreparable damage, with the underprivileged disproportionately harmed...our goal should therefore be to minimize mortality and social harm until we reach herd immunity.” The authors recommended policymakers adopt an approach they termed “focused protection”. This entails easing restrictions on low-risk groups, with the intention of allowing them to establish immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through natural infection, while simultaneously stepping up the protection of high-risk groups. For example, governments could fund short sabbaticals for vulnerable workers in public-facing jobs and provide accommodation for individuals who cannot easily maintain isolation in their own home.

Within weeks, an opposing group of experts, also numbering in the thousands, had put their names to the John Snow Memorandum. The document, named after one of epidemiology's greatest historical figures, defended the restrictions to slow the spread of SARS-CoV-2 as “essential to reduce mortality, prevent health-care services from being overwhelmed, and buy time to set up pandemic response systems to suppress transmission”. It described focused protection as “a dangerous fallacy unsupported by scientific evidence” and warned that “uncontrolled transmission in younger people risks significant morbidity and mortality across the whole population”. The memorandum concluded by asserting that “controlling community spread of COVID-19 is the best way to protect our societies and economies until safe and effective vaccines and therapeutics arrive within the coming months”.

Massachusetts General Hospital's Rochelle Walensky is one of the original signatories to the John Snow Memorandum. “The Great Barrington Declaration is predicated on the idea that you know who is going to get sick and you can somehow isolate and protect them, but there is absolutely no evidence that we can do this”, she said. She pointed out that the US Centers for Disease Control and Prevention estimates that up to 40% of Americans have some kind of co-morbidity that makes them vulnerable to the ravages of COVID-19. Identifying all these people is not straightforward. “No-one is suggesting that lockdowns should be the default position. They are a last resort. But if we just let the virus run free without mitigation strategies, such as masking, our hospitals will overflow and that would mean we would no longer be able to take care of the population's health across the board”, Walensky told The Lancet Respiratory Medicine.

Kulldorff counters that it is lockdowns that now present the greatest threat to population health. “We are seeing plummeting vaccination rates, people are not getting diabetes treatment, they are not attending for cancer screening, cardiovascular disease outcomes are worsening, and the restrictions are putting a huge strain on mental health”, he said. “These are not short-term problems—closing schools, for example, can have serious consequences that last a lifetime.” The USA has seen almost 100 000 excess deaths this year from conditions other than COVID-19. “A large proportion of those excess deaths are due to various aspects of the lockdown”, said Kulldorff. “If you are not in a vulnerable group, the collateral damage of lockdown is far more destructive than the virus.”

The drafters of the Great Barrington Declaration stress that they are not suggesting people behave recklessly. Basic precautions, such as handwashing and self-isolation, when necessary, should be maintained. But the priority is to dismantle many of the constraints that have been imposed all over the world this year. The declaration advocates the resumption of sports and cultural events and the re-opening of restaurants and other businesses. It advises young, low-risk adults to discontinue working from home.

Kuldorff and colleagues reckon a focused protection approach would lead to herd immunity some time between 3 and 6 months, after which the vulnerable could return to normal life. Walensky retorts that the herd immunity point has not been established, nor is it clear how stable this immunity would be. She noted that the 11 million infections and 250 000 deaths from COVID-19 that have been documented in the USA only constitute a small fraction of the total population. “I am not willing to stand behind a policy that leads to 10 or 15 times more deaths”, said Walensky. She would prefer to wait for herd immunity to be conferred by a vaccine. Most experts believe the earliest this could happen would be the second half of 2021. The debate over what to do in the interim looks set to continue.