A group of 80 international researchers have published an open letter condemning herd immunity strategies as "a dangerous fallacy unsupported by the scientific evidence".

The letter, published in the Lancet, says that it would be a mistake to allow Covid-19 to develop in low-risk populations while protecting the most vulnerable. Known as the John Snow Memorandum, the letter will also be launched during the 16th World Congress on Public Health programme 2020 taking place 12-16 October.  

The researchers have expertise spanning public health, epidemiology, medicine, paediatrics, sociology, virology, infectious disease, health systems, psychology, psychiatry, health policy, and mathematical modelling. 

In the letter, they say that it is critical to act decisively and urgently. Effective measures that suppress and control transmission need to be implemented widely, and they must be supported by financial and social programmes that encourage community responses and address the inequities that have been amplified by the pandemic.

Suppression of the virus until the population can be vaccinated

They added that continuing restrictions will probably be required in the short term, to reduce transmission and fix ineffective pandemic response systems, in order to prevent future lockdowns.

The authors acknowledged that ongoing restrictions have understandably led to widespread demoralisation and diminishing trust among the public, and that in the face of a second wave of infection there is renewed interest in so-called natural herd immunity approaches but they say any pandemic management strategy relying upon immunity from natural infections for Covid-19 is flawed.

They explain that uncontrolled transmission in younger people risks significant ill-health and death across the whole population - with real-world evidence from many countries showing that it is not possible to restrict uncontrolled outbreaks to certain sections of society, and it being practically impossible and highly unethical to isolate large swathes of the population.

Instead, they say that special efforts to protect the most vulnerable are essential, but must go hand-in-hand with multi-pronged population-level strategies.

We still do not understand who might suffer from 'long Covid'

They also state that there is no evidence for lasting protective immunity to Covid-19 after natural infection, and warn that this waning immunity as a result of natural infection would not end the Covid-19 pandemic but instead result in repeated waves of transmission over several years.

This is because it could place vulnerable populations at risk for the indefinite future, as natural infection-based herd immunity strategies would result in recurrent epidemics, as seen with many infectious diseases before mass vaccination. Instead, the authors call for suppression of the virus until the population can be vaccinated.

The authors also warn that natural infection-based herd immunity approaches risk impacting the workforce as a whole and overwhelming the ability of healthcare systems to provide acute and routine care. They note that we still do not understand who might suffer from 'long Covid', and that herd immunity approaches place an unacceptable burden on healthcare workers, many of whom have died from Covid-19 or experienced trauma as a result of having to practise disaster medicine.

The letter concludes: "The evidence is very clear: 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. We cannot afford distractions that undermine an effective response; it is essential that we act urgently based on the evidence."