The ‘herd immunity’ strategy for COVID-19 is dangerous and unfeasible 

herd immunity
© Al Robinson

Professor Martin Michaelis and Dr Mark Wass of University of Kent’s School of Biosciences, explain why a herd immunity approach to COVID-19 would create greater risk, potentially many deaths, and may simply not work

The idea of letting COVID-19 spread to generate “herd immunity” and end restrictions is part of the public discourse on how to deal with the pandemic. Three researchers have written and publicised the “Great Barrington Declaration”, an argument that SARS-CoV-2, the coronavirus that causes COVID-19, should be allowed to spread among low-risk groups to build up herd immunity within the population, while vulnerable individuals are protected.

This is an extremely dangerous approach, which may not work as would be hoped by those making such a declaration as it is still unclear whether SARS-CoV-2 infection may be associated with a lasting immunity.


Current data from individuals without symptoms or mild forms of the disease instead suggest that immunity is rapidly waning and there is no longer-term protection. This notion is supported by an increasing number of re-infections, including cases in which the second infection is more severe than the first one. Hence, it appears unlikely that an unhindered SARS-CoV-2 spread would result in herd immunity. Therefore, such an approach may not have the desired effect although it puts many lives at risk.

There is also discussion about exactly which proportion of the population would need to be infected to establish herd immunity, with some arguing that this could be as low as 20%. However, recent data from Brazil and Italy convincingly show that about two-thirds of a population can be infected in a first unrestrained wave. This tells us that the numbers of cases and deaths would therefore inevitably be high in the absence of control measures such as those to which we are now becoming accustomed. At an anticipated mortality rate of about 0.5%, infection of about 66% of the population would result in about 200,000 to 250,000 deaths in the UK and about 25 to 26 million deaths worldwide.

A strong argument for the unhindered COVID-19 spread is that it would cause less collateral damage to the economy, public mental health, and death by other causes. However, a COVID-19 with free reign would result in a greatly increased number of cases and hospitalisations, with the extremely daunting potential to overwhelm the health system. This is all the more likely given that health workers and hospital staff are at a high risk of infection, which cause further shortages. Therefore, an unimpeded spread would have a substantial impact on hospital capacities and the treatment of other diseases, which can resonate all the worse as we enter winter.

With high proportions of the population infected with COVID-19, a substantial number of low-risk individuals would also become severely ill. Hence, the unhindered COVID-19 spread may also affect other vital parts of the infrastructure. It is hardly conceivable that in a scenario with very high numbers of SARS-CoV-2-infected individuals, people would maintain their normal routines. In such a scenario, a large part of the population would be fearful and reluctant to continue their lives normally, which would likely result in either similar or worse effects on the economy, mental health, and the treatment of non-COVID-19 diseases as has come from existing lockdowns and control measures.

The Barrington Declaration does not provide a plan detailing how the government can isolate and protect vulnerable individuals, nor has any credible way to do this been suggested. Given that between 20-40% of the UK population have been estimated to fall into the high-risk category, this would mean isolating enormous numbers of people, which is not feasible and is of potentially greater impact to the infrastructure.

No past evidence

Finally, and most crucially, no infectious disease has ever been stopped naturally by herd immunity. The only disease successfully eradicated in humans was smallpox, after an intensive vaccination programme. Although Edward Jenner had invented the first modern vaccine in 1796, it took almost 200 years until the world was declared smallpox-free. In 1959, the World Health Assembly accepted a global initiative to eradicate smallpox. Progress was slow and in 1966 the Smallpox Eradication Unit was established, featuring international members, working till 1980 to be able to declare smallpox eradicated.

Influenza viruses that cause the ‘flu’ are anticipated to have been circulating in humans for more than 8,000 years. Nevertheless, they still cause about 150,000 to 650,000 deaths globally each year and many more during occasional pandemics, despite the availability of vaccines.

Cholera has also caused numerous pandemics over the centuries. Cholera outbreaks, caused by the bacterium Vibrio cholerae and transmitted by contaminated water, are largely prevented by improved sanitation. However, cholera poses a continuous threat in less developed countries and is estimated to cause about 3 million cases and 100,000 deaths each year. Hence, hope that an unhindered COVID-19 spread may naturally result in herd immunity, with a substantial reduction of the disease’s impact, would not seem realistic.

Taken together, ideas to establish herd immunity through the unhindered spread of COVID-19 among low-risk individuals are dangerous, unethical, and most probably unfeasible. Such an approach would put large parts of the population at an unnecessary risk and probably cause more damage than previous and current COVID-19 measures.


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