Herd immunity and lifting lockdowns: a new trolley problem?

By Ezio Di Nucci

How does pursuing herd immunity compare with lifting lockdowns, from an ethical point of view? The (moral) problem with the pursuit of herd immunity under a pandemic such as COVID-19 is that getting more than half of the population infected (the herd immunity threshold is at least 60%), given a CFR of say 1%, means having to kill at least 0.6% of one’s population. We are therefore intentionally sacrificing the 0.6% in order to achieve herd immunity.

Given some plausible non-consequentialist constraints, whatever the potential benefits of achieving herd immunity, the intentional sacrifice of 0.6% of one’s population (2 million people in the US alone, for example) is widely deemed morally wrong.

Now compare the pursuit of herd immunity with lifting the lockdown: as a result of lifting lockdowns, more people will likely die than if the lockdowns had been kept in place for longer, but that sacrifice is (currently) considered proportional by many governments given the psychological, social and economic benefits for the rest of the population.

What is the theoretical difference between pursuing herd immunity and lifting lockdowns? If you are a consequentialist, the difference might just be the size of the sacrifice given the respective benefits of the two strategies, namely the number of people who will die as a result of pursuing herd immunity as opposed to the number of people who will die as a result of lifting lockdowns.

What if you – like most people – are not a consequentialist, though? One possible non-consequentialist difference is the following: in the pursuit of herd immunity, the sacrificed 0.6% of the population are an intentional means to the end of herd immunity – the 0.6% are sacrificed in order to save the rest. Lifting the lockdown will also have the consequence that more people will die than if the lockdown had been kept in place for longer (supposedly), but those extra deaths are side-effects of lifting the lockdown rather than means to the end of the lockdown being lifted.

Those of you familiar with the so-called Doctrine of Double Effect (or at least its modern counterpart, the trolley problem) will recognize the above distinction between intended means and merely foreseen side-effects; according to most interpretations of the Doctrine, the latter kind of harm can – under certain circumstances – be allowed; while the former kind of harm – intended means – can never be morally permissible.

This trolley-interpretation of the difference between pursuing herd immunity and lifting lockdowns would fit in nicely with current political debates, where herd immunity is almost universally condemned while most countries around the world have now begun lifting their lockdowns. Could it be that the good old Doctrine of Double Effect explains and justifies what is going on at the moment with the COVID-19 pandemic?

There are two related problems with the above reading:

  • Our anti-pandemic effort had better not depend on the Doctrine of Double Effect, because there are many well-known problems with the Doctrine;
  • As it is explained below, even supporters of the Doctrine might struggle to distinguish theoretically between pursuing herd immunity and lifting lockdowns.

The problem is that if we accept that, in lifting lockdowns, the extra deaths are merely foreseen side-effects instead of intended means, it is very tempting to try to put forward the same argument for pursuing herd immunity as well: namely, it could be argued that we don’t intend nor need anybody to actually die in order to get herd immunity – it is just that we know, statistically, that a certain number of people will die in the process, just as we know that a certain number of people will die as a result of lifting the lockdown. Neither kinds of deaths are instrumental to the respective ends, while both kinds of deaths are inevitable given the respective strategies; which is another way of saying that if the Doctrine can legitimize lifting lockdowns, it will by the same light also be able to legitimize pursuing herd immunity.

The Doctrine of Double Effect, then, if it can justify anything at all, will be able to justify both (in principle anyway; because in practice that will also depend on proportionality considerations). But in fact the above difficulty in distinguishing between merely foreseen consequences – side-effects – and intended consequences – means – for the case of the COVID-19 pandemic is symptomatic of the Doctrine’s general problems hinted at under (1).

The good news is that a possible ethical argument justifying the pursuit of herd immunity has been resisted. The bad news is that we might pay a high price for it, namely the legitimacy of lifting lockdowns during the COVID-19 pandemic. And this outcome ought not to be too much of a surprise either: if we imposed lockdowns in order to save lives, can we deny responsibility for the lives lost as a result of lifting those very lockdowns?


Author: Ezio Di Nucci

Affiliation: Centre for Medical Science and Technology Studies, University of Copenhagen

Competing interests: None declared


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