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Herd immunity - myth and reality

30 November 2020

While many scientific myths have emerged during the course of the global pandemic the most prominent and persistence of these has undoubtedly been that of “herd immunity”.  Its basic proposition is that by allowing the virus to spread among sections of the population that are considered least susceptible to severe illness a level of immunity can be built up that breaks transmission and protects the population as a whole.  The implication of this in terms of public health policy is a rejection of restrictive measures such as lockdowns.  This certainly has an appeal to governments and most of them - to one degree or another - have adopted a strategy that is influenced by the herd immunity approach.  Given the negativity surrounding the concept, this is never admitted publicly.  It is usually given the softer framing of “Living with Covid” (a phrase which has been adopted by the Irish government).  A blunter version of this is the recent admission from the Trump administration that it was "not going to control the pandemic".

History of herd immunity

One of the reasons for the persistence of the herd immunity myth is that it has some resonance as a scientific concept.  It originated within American veterinary science in the early 20th century around the phenomenon of “contagious abortion”—epidemics of spontaneous miscarriage—in cattle and sheep.  By the 1910s, it had become the leading contagious threat to cattle in the USA.   The standard means to deal with this was for farmers to destroy or sell affected cows.  However, Kansas veterinarian George Potter realised that this was the wrong approach.  As an alternative he proposed an approach to the disease which he characterised as “herd immunity”.  In an article written in 1918 he described it is the following terms:

 “Abortion disease may be likened to a fire, which, if new fuel is not constantly added, soon dies down. Herd immunity is developed, therefore, by retaining the immune cows, raising the calves, and avoiding the introduction of foreign cattle.”
This concept was developed further in subsequent years.  In an article in the Lancet in 1919 bacteriologist W W C Topley described experimental epidemics he created in groups of mice. He observed that unless there was a steady influx of susceptible mice, the rising prevalence of immune individuals would end an epidemic.  The idea moved into medicine in 1922 when Topley suggested a parallel between outbreaks in mice and children.  It was advanced further by Sheldon Dudley, professor of pathology at the Royal Naval Medical School, who had become aware of epidemics of diphtheria while working at the Royal Hospital School in Greenwich. In a 1924 article in The Lancet, Dudley applied “herd immunity” to humans. In a 1929 article, “Human Adaptation to the Parasitic Environment”, he wrote,
“I will now consider the community, or the herd…Nations may be divided into urban or rural herds. Or we can contrast the shoregoing herd with the sailor herd, or herds dwelling in hospitals can be compared with those who live in mental hospitals.”
By the 1930’s “herd immunity” had become a fixture of epidemiology with discussion of the concept in relation to influenza, polio, smallpox, and typhoid appearing in textbooks, journals, and public health reports.  In that period, similar to what we see today, it was an idea that could be co-opted into right wing ideology.  At a time when eugenic racism was in the ascendancy it regularly intersected with notions of racial difference/inequality.  For example, an author of a 1931 Lancet piece wondered whether specific groups had “racial herd-immunity”.

Herd immunity – or “population immunity” as it had become known – gained prominence once again in the 1950s and 60s with the development of new vaccines.  This raised critical questions for public health policy around what share of a population had to be vaccinated to control or eradicate.  In the period since 1990, in which epidemics (and pandemics) have become more frequent, public health officials have worked to achieve population immunity through sufficient levels of vaccine coverage.  The critical point here is that – for the last sixty years – population immunity has been incorporated within the framework of mass vaccination.  Proponents of “herd immunity” as strategy to contain Covid break with modern medical orthodoxy and instead revert to an older and cruder version of the concept that is closer to animal husbandry than human health.

The Great Barrington Declaration

The most high-profile presentation of the herd immunity approach is the Great Barrington Declaration.  This declaration, authored by Dr Jay Bhattacharya, Martin Kulldorff (both of Harvard) and Sunetra Gupta (Oxford University) - and supported by thousands of signatories who identify as science or health professionals - calls for allowing the coronavirus to spread naturally in order to achieve herd immunity.  Its central proposition is that to contain the coronavirus, people “who are not vulnerable should immediately be allowed to resume life as normal” while those at high risk are protected from infection.  Younger and healthier people would be encouraged to return to work and to socialise while the elderly and those with underlying health conditions would remain shielded.  It is claimed over time so many people in the former category will have been exposed, and developed some immunity, that the virus will not be able to maintain its hold in the population.  In this scenario there is no need for lockdowns.  Indeed, all mitigations (except shielding) are rejected as they would slow the spread of the virus and delay the achievement of herd immunity.

The appeal of this approach is obvious both to governments and to various commercial interests so it is no surprise that they would promote the Great Barrington Declaration.  The day after the declaration was made public, the three authors met Trump administration officials for a briefing.  Commenting on the meeting the health and human services secretary, Alex M. Azar II, said: “We heard strong reinforcement of the Trump Administration’s strategy of aggressively protecting the vulnerable while opening schools and the workplace.”

It is no co-incidence that the Declaration was commissioned and published by the American Institute for Economic Research. a think tank dedicated to free-market principles.  Its partners include the Charles Koch Institute (founded by the billionaire industrialist) which for some time has been the principal financial supporter of organisations that have prompted climate change scepticism.  Indeed, there is a great degree of overlap, in terms of organisation and financing, between the climate change and Covid scepticism movements.  They also have a similar mode of operation. Central to this is the promotion of a dissenting opinion in order to create the impression that there is an ongoing debate within the scientific community over these questions rather than a settled consensus.

All of this illustrates that science – despite its materialist conception of the world - does not stand outside of the class structure of society.  It can be used for oppressive ends and can also be distorted to support class oppression.  Herd immunity, as a justification for the normal operation of capitalism through the pandemic, falls into this latter category.


While the political and commercial associations of the proponents of herd immunity should raise suspicions this in itself is not enough to counter their arguments.  It is important that they also be refuted on the basis of medical science.

The biggest flaw within the herd immunity proposition is the assumptions around the spread of the virus and the achievement of immunity.  The main assumption, that the spread of the virus through the population will produce the rate of infection (and acquired immunity) required to break transmission, has no basis in fact.  It is estimated that the achievement herd immunity would require 60-70% of the population to have been infected and to have acquired immunity.  However, seroprevalence studies* – including in countries** where the virus has been allowed to spread – have shown a low a low level of population immunity (usually around 10% rising to 20% in hotspots).  It is a long way from the level that is assumed for herd immunity.  If population immunity where to be achieved by this method the consequence would be much greater numbers of people becoming ill and dying.  Even under the current conditions - with many mitigations in place – there have been one and half million deaths worldwide in the space of nine months.  What would the number have been had herd immunity been pursued as a consistent strategy across the globe?

The other major flaw is the assumption that sectors of the population (such as the elderly and those with underlying health conditions) who are most susceptible to severe illness can be shielded.  This assumes that people who are in the vulnerable category are a relatively small percentage of the population and that they can easily identified.  However, neither of these are true.   The percentage of people in the vulnerable category is actually quite high (up to 30% of the population) while the range of health conditions (diabetes, high blood pressure, obesity etc) associated with a severe reaction to Covid is wide.  This makes shielding very difficult – even more so in circumstances where the virus is running uncontrolled through the population.  There is also a lack of practicality with these shielding proposals.  They fail recognise the reality of peoples’ living conditions particularly of the poorest families who are more likely to live in multi-generational households.  Such a strategy would require people in the vulnerable categories to move away from their families or to risk having younger family members bring the virus home.  This ignorance - or indifference - may well be a reflection the class prejudices of the advocates of these proposals.

The two main propositions within the herd immunity approach – of allowing the virus spread while shielding the vulnerable – stand in contradiction to one another.  The reality is that a higher prevalence of the virus (which is necessitated by herd immunity) creates a greater risk to those that are most susceptible to severe illness and potential death.

Another unstated assumption of herd immunity is that people who recover from the virus make a full recovery.  However, studies have found that about a third of people who have recovered from the disease, including those in younger age groups, still struggle with symptoms weeks later.   At this stage it is still unclear what the long-term health effects will be.  All of this makes a herd immunity approach to the coronavirus pandemic extremely reckless.  It has been described by public health experts who endorsed the John Snow Memorandum (a response to Great Barrington) as a “dangerous fallacy unsupported by scientific evidence”.


In the period prior to mass vaccination the only method to tackle the pandemic is to suppress the virus; bring it under control; and keep it under control.  Mitigations will certainly be part of this as will an effective system of test and trace.  This is the type of public health policy that workers should be demanding.  It is both practical and scientifically sound.  Most importantly we know that it works because it has worked in countries (South Kora, New Zealand etc) where it was deployed.  The capitalist barbarism expressed in the pseudo-science of herd immunity, in which people’s lives are expendable, must be rejected.


*Seroprevalence studies use antibodies as markers of pathogen exposure to estimate the proportion of the population that has been infected.  Studies conducted in relation to coronavirus have also cast doubts over the strength of the immune response and the length of time it lasts.

** Sweden is usually held up as the model for a herd immunity strategy.  While Swedish health officials have denied that, it is certainly true that they had a less restrictive regime in place and had also promoted the idea of a slow burn of the virus through the population.   However, the results were not good with Sweden recording a higher infection and death rate than its neighbours.  The argument that this initially worse outcome would be compensated for by the avoidance of a second wave has also been disproved with the virus once again surging.

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