A term has been gaining steam in COVID-19 mitigation lexicon: “Zero-COVID.”

Should countries be aiming for this lofty goal?

A recent Rapid Response letter published by Emeritus Professor of Public Health Raj Bhopal in BMJ argues that we should.

Bhopal also, however, argues the taboo point that population immunity will likely need to come from a combination of vaccine and naturally acquired immunity.

“Of course, everyone wants this,” Bhopal writes of COVID-19 elimination, “but the big question is how to achieve it and at what cost, not just monetary but in terms of health, educational, social and other sacrifices.”

Bhopal recently published a comprehensive public health strategy in the journal Public Health in Practice.

The article is named “COVID-19 Zugzwang” after a situation in chess where players must choose between several unappealing options. It outlines efforts such as social distancing, hygiene improvements, contact tracing, vaccine development, and treatment.

But to these public health measures Dr. Bhopal also adds that we must take a more controlled approach to the naturally occurring phenomenon of so-called “herd” or population immunity.

“I return to the subject of herd immunity which has become taboo for political, not public health, reasons. I have recommended we change the terminology to population immunity to allow a fresh start given the understandable antipathy to the world herd which evokes visions of cattle and other animals,” Bhopal explains.

Population immunity is already developing in a segmented but uncontrolled way, according to Bhopal. And this development does not necessarily contradict the search for a vaccine or any other needed public health measure.

The original Zugzwang paper originated when Professor Martin McKee wrote to a COVID-19 Global Research e-mail list Bhopal belongs to seeking “sensible thoughts” on the difficult matter of an exit strategy out of “lockdowns.”

Bhopal’s 8-point plan relies on fundamentals of public health. It also argues that if there is no sign of an imminent vaccine with mass uptake, the scientific community must at least consider allowing younger people from the least vulnerable demographics on a voluntary basis to live their lives more normally, perhaps getting the infection in more controlled circumstances.

This is particularly true in low- and middle-income countries with young populations that face other infectious disease burdens than COVID-19. Several countries with demographic factors like Pakistan or Kenya have seen lower infection fatality rates than the western world thus far.

In all countries, severe infection has been overwhelmingly concentrated amongst older individuals. Despite media emphasis on outliers, or on frightening anecdotes, this is the case statistically.

Bhopal acknowledges the recklessness of proceeding without a plan, though.

“The needs of wider society, not just the elderly but also others at high risk or those living with people at high risk, need to be thought through simultaneously,” he writes.

Bhopal argues that the population immunity process is already, in effect, being implemented in an uncontrolled and haphazard way across the world, especially in countries like Brazil that have neglected a response broadly.

“In my paper I emphasize that letting the pandemic unfold (rip in the media parlance) randomly is not part of any public health strategy.”

As an estimate, Bhopal suggests that roughly 40-50% population immunity is sufficient to substantially suppress an infection with a reproduction number of about 1 or slightly more.

Some consider the population immunity threshold to be as low as 25%, but Bhopal opts for a more conservative estimate and advocates for a highly age stratified approach with targeted protective interventions for the vulnerable.

“Allowing infection in those at very low risk, in my view, can be justified if we make it safer for them than allowing it to occur uncontrolled as is seemingly inevitable. Importantly, in children and young people COVID-19 is currently rarely fatal, and less so than influenza for which we already have a vaccine, even in the recent period from March-June, which is probably the worst we will go through.”

A vaccine may be rolled out with sufficient safety standards, but given the visible rush to end the pandemic, public health trust may be another matter.

To reach zero-COVID, Bhopal argues we will inevitably need to acquire population immunity through a combination of control measures including vaccination and the already-occurring sectional acquisition of immunity through natural infection.

Interview: Raj Bhopal on our next move in the COVID-19 "Zugzwang"

Raj Bhopal, CBE DSc, BSc MD, MPH, MBChB, FRCP, FFPHM, is professor emeritus of public health at the University of Edinburgh, Scotland. He held the chair of Public Health in the university until his retirement in 2018.

Bhopal is also the author of Concepts of Epidemiology: Integrating the Ideas, Theories, Principles, and Methods of Epidemiology.

Bhopal’s recent article, COVID-19 zugzwang: Potential public health moves towards population immunity, was published in Public Health in Practice.

Public Health in Practice is an official journal of the Royal Society for Public Health and a sister journal of Public Health.

The article proposes a full suite of COVID-19 interventions. It also argues, saliently, that scientific inquiry around various SARS-CoV-2 interventions has been frustrated by an unappealing mix of competing ethical priorities societies face, alongside political battles over terms like “herd immunity.”