Age-selective mixing to control the COVID-19 epidemic – still relevant in 2021?

James M Trauer, Ben J Marais, Romain Ragonnet, Bridget M Williams, James Cameron, Julian Savulescu.

In a previous blog and now feature article in JME we explored the ethics of selective liberty restriction of the vulnerable. In that paper, we considered whether differential liberty restriction could be ethically justified. Here we consider the complementary public health justification for not only protecting the vulnerable, but using age-selective mixing to achieve herd immunity. While the scientific basis of this strategy is the subject of another paper, here we explore the public health rationale.

When a novel coronavirus jumped between species in late 2019, it was met by a world accustomed to pandemics of moderate severity and no living memory of the devastation of influenza a century earlier. Preparedness guidelines from prior to 2019 focused on influenza and considered non-pharmaceutical interventions, including school closures, hygiene measures and physical distancing. However, the need for extensive society-wide lockdowns, including business closures, curfews and stay-at-home orders, was barely anticipated.

Even before the WHO declared a pandemic, it was obvious that global eradication was infeasible and the world would need to live with a new endemic infection. As the pandemic progressed, it became apparent that even a virus with an infection-fatality rate below 1% could still overwhelm health services – and even a basic reproduction number around 2-3 could necessitate substantial non-pharmaceutical interventions to achieve suppression. The tensions between the need to mitigate the direct health consequences of the virus and to avoid damage to society and the economy played out differently in every country. However, the lack of a clearly articulated pandemic control strategy has been almost universal – for example, Australia’s success in eliminating the virus nationally has been characterised by a reluctance to embrace “elimination” as a description of its approach. In more heavily impacted countries, a commoner response has been that of intermittent blanket lockdowns when surges in transmission threaten to overwhelm hospital capacity.

When it emerged that the infection fatality rate in younger age groups was negligible, it seemed that targeted non-pharmaceutical interventions could be deployed to minimise the adverse societal impacts of the epidemic. Not only are children clearly far less susceptible to the worst outcomes of COVID-19, but most evidence suggests a considerably lesser contribution to propagating the epidemic. Perhaps if transmission could be concentrated in younger persons and the elderly effectively shielded from infection, herd immunity could be achieved through natural infection without overwhelming health services?

Vaccines for animal coronaviruses and for such critical human infections as HIV and TB pursued unsuccessfully for decades – and as epidemics exploded it seemed possible that population protection through vaccination would be impossible within a reasonable timeframe, and that controlled transmission could be the only reasonable pathway back to normality. Fortunately, vaccine development and roll-out has exceeded expectations in many countries and this situation has not eventuated, increasing the theoretical and ethical dilemmas associated with a targeted natural infection approach.

Although rapid roll-out of effective vaccines provide pathway back to normality without needing to employ such a strategy, few countries are in a position to execute this in the short term, increasing the need to carefully consider how infection is allowed to spread.

The relative protection from natural and vaccine-derived immunity will become clearer over the coming months, but current immunological evidence suggests that natural and vaccine-derived immunity are broadly comparable in strength and short-term durability and should have similar population impacts on the epidemic. However, longer-term durability and the protective efficacy against newly emerging variants remain uncertain. The failure of apparently broad population-wide natural immunity fully to protect the Brazilian city of Manaus from a devastating second epidemic has shaken confidence in the ability of natural immunity to achieve effective herd immunity. This appears to be largely attributable to a new variant with significant immune-escape properties, although whether this will undermine natural immunity more than vaccine-induced immunity remains unclear.

Despite the clear need to protect the elderly in the Australian state of Victoria during Australia’s second wave, the epidemic became particularly concentrated in residential aged care facilities and attempts to protect the most vulnerable in our society were no match for the structural obstacles presented by a long-neglected sector. Countries and cultures differ markedly in their approach to caring for their elderly, and in the face of renewed epidemic outbreaks in areas with limited vaccination coverage, the question of how ‘elderly protection’ may best be achieved remains relevant in many settings?

Moreover, the sometimes crippling post-infection sequelae (“long-Covid”) remain to be fully quantified, but are essential to acknowledge and should be considered in any approach that permits significant community transmission.

Much remains to be learnt and doubt persists as to whether community transmission can be ‘directed’ towards the least vulnerable members of the community, whether herd immunity through natural infection can be achieved and the extent of harms inflicted along the way. However, as the global case and death counts continue to soar, it is inevitable that millions more will be infected and more societies and economies crippled through lockdowns before the end of the pandemic. In this context, the question of how to best mitigate transmission through non-pharmaceutical interventions remains pertinent, and clear-minded national strategies are as important as ever.

This is particularly the case in low-income settings that are scrambling to vaccinate their populations with limited vaccine supply, while high-income countries ensure they receive the lion’s share of globally available vaccines. In such low-resource settings, where a day of lost income has dire consequences for poor families, sustained lockdowns may be as devastating as the epidemic itself.

In the face of substantial transmission, some aspects of any strategy should be routine, such as face coverings, physical distancing, personal hygiene and working from home where possible. However, substantially greater measures are often needed to achieve a significant impact on the epidemic trajectory. Achieving this with the lowest possible societal impact and with the lowest possible rates of transmission among the most vulnerable groups should remain an active area of investigation.


Paper: The ethics of selective restriction of liberty in a pandemic

Authors: *James Cameron, 2, 3 *Bridget Williams,4 Romain Ragonnet,4 Ben Marais,5 James Trauer,4 Julian Savulescu 1, 2, 3

* Joint first authors


1: Oxford Uehiro Centre for Practical Ethics, Faculty of Philosophy, University of Oxford, Oxford, UK.

2: Murdoch Children’s Research Institute, Melbourne, Australia.

3: Melbourne Law School, University of Melbourne.

4: School of Public Health and Preventive Medicine, Monash University, Australia

5: Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney

Competing interests: None declared

Social media accounts of post authors@bridgetw_au @juliansavulescu

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