The Hard Truth of Herd Immunity

Experts ignored science and redefined medical terms to promote vaccines and destructive public health policies.

12 minute read

If I had to pinpoint a date when the COVID-19 response went haywire, it would be March 16, 2020. That was the day Imperial College London released its infamous “Report 9” which grossly overestimated the risk of the virus and the effectiveness of lockdowns in suppressing viral spread. Before nightfall, the UK government caved to pressure and swerved from a sensible and realistic strategy based on basic epidemiological principles and decades of pandemic planning.

From then on the British government – like governments elsewhere – became increasingly draconian and trapped itself and its population in an endlessly escalating and self-reinforcing spiral of ineffective and socially destructive public health measures. In retrospect, it was a futile attempt to wage a war on a virus. By extension it became a war on those it would inevitably infect: all of us.

Central to that policy shift was a disavowal of herd immunity.

The displacement of reason by panic started becoming apparent a few days earlier on March 13, when epidemiologist and government advisor John Edmunds appeared on Channel 4 News. During the segment, Edmunds explained the role of herd immunity in the British government’s strategy. He was opposed by Thomas Pueyo, a Silicon Valley marketing executive who rose to media fame during COVID for his blog littered with pandemic hot takes.

Pueyo now brands himself a journalist and his recent commentary ranges from critiques of the German and Japanese economies, space travel to Mars, and a personal opinion on where the United States should build future cities. That a British news channel would have marketing executive Pueyo debate epidemiologist Edmunds on epidemiology foreshadowed the coming break from reason.

In the interview, Edmunds pointed out that there are two strategies with a new virus:

One, you can stamp out every single case in the world—every single case in the world—and then you’re free. You’ve stopped the epidemic without achieving herd immunity but you must catch every single case in the world. […] That’s the phase that we were in when we were trying to do containment, and everybody else was trying to do containment. It hasn’t worked.

Of course, this strategy only works if you can identify every person who is sick and the virus has not spread that much. But Edmunds correctly noted that “the genie is out of bottle” as the COVID virus was already spreading around the world. At this point, “herd immunity” becomes central to any strategy to mitigate the pandemic. Critical here is the related concept of the “herd immunity threshold”: when enough people have been infected and are immune that the spread of the virus begins to slow down. Edmunds explained:

The natural way that this will happen is that the epidemic will run very fast and the epidemic will come up and come down very fast. And the herd immunity threshold is reached not at the end of the epidemic – that’s what people sort of think – it’s not at the end of the epidemic. It’s at the peak of the epidemic. At that point there’s not enough susceptibles in the population to spread.

Edmunds’ point was that the epidemic would ultimately recede when a critical mass of people had become immune – i.e. when the herd immunity threshold was reached. Crucially, this would happen before everyone had been infected, offering the possibility of shielding vulnerable people as others went about their lives and acquired the immunity that would help protect vulnerable people into the future.

Though many global experts would later redefine the herd immunity threshold as a mystical panacea that could only be achieved through mass vaccination that banished the virus forever, this is not what it means. A 2008 epidemiology textbook defines the herd immunity threshold exactly as Edmunds explained it:

The proportion of immunes in a population, above which the incidence of the infection decreases.

- Porta, A Dictionary of Epidemiology (Oxford University Press, 2008), p. 115

Note that infection “decreases.” Infection does not, as too many TV experts later opined, “disappear” with herd immunity. The herd immunity threshold is not synonymous with disease elimination.

The same day that Edmunds articulated the accepted approach to managing a pandemic on national television, the UK’s Chief Scientific Advisor, Sir Patrick Vallance, echoed what Edmund’s said. In a meeting of high-level British officials, Vallance stated the goal:

try to reduce the peak, broaden the peak, not to suppress it completely. Also, because most people, the majority of people get a mild illness, to build up some degree of herd immunity as well so that more people are immune to this disease and we reduce the transmission. At the same time, we protect those who are most vulnerable from it.

Many advisors would later deny outlining such a strategy, yet Edmunds and Vallance explained very clearly that infection-acquired herd immunity would be the brake that would slow the epidemic, transforming it into a more manageable, endemic illness. Until this point was reached, we had to protect the vulnerable from infection. Vulnerable people’s “immunity” would come from a ring of protection provided by the rest of us who became infected and immune while going about our lives.

Going to work, taking the kids to school, participating in social events: these were not anathema to managing the pandemic. They were essential to managing the risk collectively. Later on, treatments and a vaccine might offer the vulnerable more durable protection, but in the meantime: Keep calm and carry on.

This strategy was perhaps best articulated by professor Graham Medley, Edmund’s colleague at the London School of Hygiene and Tropical Medicine. On the same day that Edmunds spoke to Channel 4, Medley went on the BBC and noted that “we’re going to have an epidemic and then it will become endemic and join in with all the other coronaviruses that we all have all the time, but don’t notice.”

Again, Medley said this three days before Imperial College released “Report 9” which completely upended the UK’s strategy on March 16, 2020. Medley offered this thought experiment:

Ideally, if I could, what I would like to do is to put all the more vulnerable people into the north of Scotland and keep them there, everybody else into Kent [i.e. far away from northern Scotland] and have a nice big epidemic in Kent, so that everyone becomes immune, and then we can put people back together again. But we can’t do that. So what we’re going to have to try and do ideally is some kind of manage this acquisition of herd immunity and minimize the exposure of people who are vulnerable.

As Medley explained, herd immunity is not a choice or a “strategy,” as others would later insist. Much like gravity explains why an object falls to earth, herd immunity explains why epidemic waves inevitably fall before everyone is infected. Tragically, some people were going to die, “there’s no way out of that now,” as Edmunds candidly put it. But perhaps, if we kept our heads, we might have been able to limit vulnerable people’s exposure to the virus, since they were the most at risk of dying.

A week after the UK government pivoted away from herd immunity, epidemiologist and future advisor to President Biden, Michael Osterholm, wrote an essay in the Washington Post that also promoted herd immunity while criticizing lockdowns: “Facing COVID-19 reality: A national lockdown is no cure.”

Even mentioning the term “herd immunity” will get you castigated as unscientific in the media today, but editors at the Post had not yet capitulated to this rule in March 2020. Here’s what they allowed Osterholm to write:

COVID-19 will go away eventually in one of two ways. Either we will develop a vaccine to prevent it, or the virus will burn itself out as the spread of infection comes to confer a form of herd immunity on the population.

Osterholm added that the more reasonable strategy than prolonged lockdown was to “gradually build up immunity” by letting “those at low risk for serious disease continue to work” while shielding higher risk individuals.

By May 2020, however, the accepted definition of herd immunity had been fully revised. During a press conference, the World Health Organization’s Mike Ryan falsely stated that herd immunity “is normally a phrase that's used when you think about vaccination.” Ryan’s newfangled description completely ignored that herd immunity also includes immunity developed through infection. Yet, he continued to promote vaccination as the only path to ending the pandemic.

“Humans are not herds,” Ryan said, attempting an awkward joke. He then falsely asserted again, “And as such the concept of herd immunity is generally reserved for calculating how many people would need to be vaccinated in a population in order to generate that same effect.”

With international experts now redefining herd immunity as a mystical elimination threshold achieved exclusively through vaccination, it was not unexpected that The Lancet soon took Medley to task for having dared warn that eventually everybody would be infected. In a sign of escalating irrationality, the prestigious medical journal misquoted Medley’s March 2020 BBC interview to imply he had said that herd immunity meant he simply wanted “a nice big epidemic.”

Since that day we have been endlessly lectured that herd immunity without a vaccine really means “let it rip” and is code for sacrificing the vulnerable to save the economy. After promoting herd immunity and opposing lockdowns in March, that August Michael Osterholm pulled a 180 and called for lockdowns in the New York Times.

The definition for herd immunity was further shaped following the October 2020 release of the Great Barrington Declaration which outlined a strategy of “focused protection” to better protect the elderly and other high-risk groups, while allowing others to continue their lives. Responding to the proposal, the WHO’s Director General, Tedros Ghebreyesus, then inaccurately claimed that herd immunity “is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached.”

Yet Tedros’ statement directly contradicted the WHO’s own definition of herd immunity. At the time, the WHO defined herd immunity just as others did: “the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection.”

A couple of weeks after Tedros made his inaccurate remarks, the WHO changed its definition of herd immunity, removing mention of immunity from infection, and promoting vaccination. Following criticism, some of the original meaning was later added back.

The WHO’s online revision of herd immunity serves as a case study of the expert class’s disingenuous denunciation of herd immunity and helps explain everything that followed. The futile mass testing of healthy people. The months and years of school closures. The loved ones dying alone in “care” homes so they didn’t pass on the virus. The “Zoom funerals.” The masking. The double masking. The vaccine mandates for those least at risk.

So much of this flowed from denial of the fundamental underlying reality that few wanted to acknowledge after March 16, 2020: the epidemic would only recede when enough people had been infected and developed immunity. The only question that mattered was: As the pandemic unfolded, who should we protect?

That question was thrown out once herd immunity was cast aside as irrelevant, dangerous, and “anti-science.”

Prominent experts are now on the record denying the historical and biological reality that respiratory pandemics end through the accumulation of immunity in the population. Their repudiation of herd immunity was fundamentally a repudiation of our social bonds. Disavowing the idea that we were all part of a larger social collective – yes, a “herd” – was the first step down a path to viewing our fellow humans as little more than biohazards to be avoided at all costs.

Inevitably, public health, which should be concerned with the health of the public, became a divisive competition pitting individuals against each other. But those most at risk – frail elderly people in care homes – were least able to compete at this game. Like the millions of children denied education and socialization following the disavowal of herd immunity, the elderly were sacrificed at the altar of “infection control.”

Everything after made sense once we had accepted the premise that we could only be safe by accepting a “new normal” in which we stayed away from each other and showed “solidarity” by banging pots and pans on the balcony (if you were fortunate enough to have a balcony).

Even a brief review of epidemiology textbooks makes obvious the lie that herd immunity is purely about vaccination. It has been a staple concept of infectious disease epidemiology since the early 1920s, when British scientists realized that epidemic waves were better explained by the accumulation of immunity in the population than presumed changes in the pathogen’s virulence.

Summarizing almost two decades of this work, these scientists argued in 1936:

In any of those common endemic-epidemic diseases from which many or most of our people suffer at one time or another during their lives, but which occur in epidemic form only at more or less widely-spaced intervals, we should regard this ever-varying state of the immunological constitution of the herd as the main factor determining the intervals at which the epidemic waves occur.

Nor is this some outdated interpretation of the concept as it was defined before Pfizer and Moderna invented the politically correct – and highly profitable – way to obtain immunity—boost, boost, BOOST! A textbook published just a few years before COVID defined herd immunity:

Individuals who develop immunity to an infectious disease, either through immunization or recovery, serve as bodyguards against the spread of that disease within their community.

- Schneider and Lilienfeld, Lilienfeld's Foundations of Epidemiology (Oxford University Press, 2015), p. 48

People immune from infection are bodyguards, not biohazards. We’ve understood this over for over 100 years.

Following the far more devastating influenza pandemic of 1918-19, the British government found that our collective immunity both explains the wave-like ebb and flow of epidemics and offers the possibility of tipping the balance in our own favor. Exactly a century before the declaration of the COVID-19 pandemic, the UK’s Ministry of Health report of the Spanish Flu noted:

the essential solidarity of all mankind in the matter of epidemic sickness. […] No sanitary cordon, no quarantine, will shield us from this danger. […] To realise that the material well-being of the inhabitants of a foreign – perhaps even a hostile – country is a pressing concern of ours is very hard. Yet the teaching of this pandemic is that it is a hard truth.

A hard truth indeed.

As more and more revisionist articles are written by reporters who either towed the line or remained silent during the pandemic, we should remember that everything we needed to know about herd immunity for COVID-19 was already known well before the pandemic started.

Back on March 13, when Medley was explaining to the BBC why herd immunity was so fundamental, he also weighed in on school closures.

When the children are not in school someone has to look after them. So either people are pulled out of work to look after their kids, or else you find somebody else to look after your kids. So parents look around and the obvious solution is grandparents, in many cases. And so you end up with a situation where you’re actually creating the kind of mixing you exactly want to avoid. And so I think closing schools will stop a little bit of transmission between the children, who are not vulnerable, but potentially increase the transmission to the vulnerable section of the population.

All the lies, misunderstandings, and disavowals of herd immunity were, in truth, misguided projections made by those who wanted to forget all the things we knew at the pandemic’s beginning. Instead they made our existence about nothing more than the COVID virus.

Just as it was “libertarian” to suggest the government should protect the vulnerable and “fringe epidemiology” to discuss a basic fact like herd immunity, today it is no doubt “anti-science” to point out these lies and demand those who told them be held accountable.

David Robertson is a historian of science and medicine. He has previously written about COVID-19 for The Washington Post, The BMJ, The Boston Globe, STAT, and The American Journal of Public Health.