November 24, 2023 - 6:00pm

This week the Covid Inquiry touched upon one of the most publicly contentious and yet fundamental concepts of the pandemic: herd immunity. Yet during questioning the Chief Medical Officer for England, Prof. Chris Whitty, perpetuated several unfortunate misconceptions about this basic epidemiological concept. 

Whitty’s position this week was that herd immunity is a concept too difficult for the public to grasp and too amenable to misinterpretation. As he told the Government in March 2020, “this is very complicated — please don’t talk about it”. Singling out the Great Barrington Declaration, he branded herd immunity a “dangerous” and “clearly ridiculous” policy approach that should not even be subject to a respectful scientific debate. It is worth, then, looking at several common misconceptions which Prof. Whitty and others continue to spread.

Firstly, Whitty, together with prominent global public health authorities such as the WHO and Anthony Fauci, continues to frame herd immunity as something that can be sustainably “achieved” and held constant rather than a dynamic relationship between susceptible and recovered populations. This new redefinition of the concept is based on diseases like measles, polio and smallpox, where durable vaccines can effectively eliminate a disease. Yet this vaccine-centric perspective isn’t valid for diseases like Covid. Rather, as a mathematical principle, the herd immunity threshold is achieved whenever the rate of infections declines due to a large fraction of the population being immune. Arguing against herd immunity is like arguing against gravity or fluid dynamics. 

Secondly, the mainstream position oddly accuses others of “deliberately spreading Covid” whilst ignoring the fact that most people on earth, including in Antarctica, have already been infected. The virus did “spread through the population”, despite two years of unprecedented Government infection control mandates in the UK. Aggregating data at national level also obscures how the virus spreads through local contact networks, with different population densities, living conditions and social interactions. The rate of transmission is not a universal constant, whatever is alluded to in the media. 

Thirdly, those who railed against herd immunity claimed that it could never be achieved because there was no lasting immunological protection from infection. This is mathematically incorrect. Herd immunity is established separately from the rate of loss of infection-blocking immunity. Coronaviruses are known to reinfect individuals at regular intervals of a few years, but the first infection confers durable protection against severe disease. Protection from severe disease was also provided from cross-immunity from previous exposure to other coronaviruses, such as the common cold. Interestingly, this implies global travel protects the human herd from a more devastating pandemic. 

In the case of respiratory viruses, epidemics are strongly influenced by seasonality (which isn’t well-defined in non-temperate countries). In fact, epidemic trajectories can be explained largely by looking at the arrival time of Covid, which explains the “waves” in winter and the fact that lifting lockdowns did not significantly increase infections in the summer of 2020. 

Finally, the ecological framework of herd immunity challenges the command-and-control infrastructure and anthropocentric hubris of government Covid mandates. This is perhaps the most threatening dimension: that two years of heavy-handed restrictions on basic social life and community caused immense social harm but were not altogether effective at controlling the pandemic, despite the models which generated an illusion of certainty. Rather, there are natural laws at work governing the human-microbial-environment interaction beyond our control. Here, human illness and death are an intrinsic yet unfortunate reality that, although minimisable by protecting the most vulnerable as with the Swedish approach, cannot be avoided altogether. Lockdowns were always a porous intervention. 

So there is still much to learn about herd immunity and respiratory pandemics. However, we must move beyond the emotive polarisation of basic epidemiological science. Government scientists such as Prof. Whitty continue to misrepresent herd immunity, and their statements have become part of the mental scaffolding which justified the UK’s emergency state. Paradoxically, these same scientists advocated for “herd immunity” and focused protection right before flipping to Plan B on 23 March, 2020.

It is time we rehabilitate the reputation of herd immunity as a foundational reality of epidemiology. Future respiratory pandemic response depends on it.

Kevin Bardosh is a research professor and Director of Research for Collateral Global, a UK-based charity dedicated to understanding the collateral impacts of Covid policies worldwide.