Three Harm‑Based Arguments For A Moral Obligation To Vaccinate Part 2

The Obligation Below the Threshold

The argument that obligations to vaccinate are strongest around the herd immunity threshold leaves us with a counterintuitive implication. If there are a significant number of non-vaccinators who spurn their obligation to contribute to herd immunity, thus moving us further away from the herd immunity threshold, the obligation to vaccinate becomes weaker for everyone. The intuition should rather be, it seems, that if there was a concerted effort by a non-vaccinating group to lower the vaccination rates in a population, the obligation to vaccinate should become stronger for others.

The herd immunity threshold refers to how many people in a group acquire immunity after being infected by a vaccine or disease, which can effectively prevent the virus from spreading in the group. In other words, as long as this threshold is reached, the virus cannot spread in the group, thus forming herd immunity.

Immunity refers to the ability of a person's immune system to protect against specific pathogens, usually acquired through vaccination or natural infection.

Herd immunity thresholds are closely related to immunity because only enough people in the human population acquire immunity to prevent the spread of an epidemic. Herd immunity is achieved when more people gain immunity and fewer opportunities for the virus to spread.

Therefore, increasing the immunity of the population (either through vaccination or natural infection) can help reduce the rate at which the disease spreads and help to reach herd immunity thresholds.

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In this section, we argue that aside from the obligation to contribute to a population-level effect to minimize the risk of harm to the vulnerable, we should also make sure that we do not cause significant harm to those around us, provided this comes at no significant cost to us. This obligation is strengthened, we contend, because the lower vaccination rates are, because there will then be more of those susceptible to disease, and consequently, we will be more likely to transmit deadly pathogens to others. To argue for a stable harm-based obligation to vaccinate below the herd immunity threshold, we must accept, or so we claim, both the collective obligation to establish herd immunity elaborated in the previous section and the obligation that we do not harm others, which we elaborate here.

The basic argument is simple. Although my contribution to herd immunity might be insignificant, given inadequate contributions by others, my infectiousness could still be decisive in whether a particular person will become dangerously infected, possibly causing that person significant harm [17: 551]. Since it would be wrong for people to expose others to the risk of significant harm, they must vaccinate, thus curbing their (prospective) infectiousness better than they would otherwise be able to. Admittedly, the chances that we would transmit infection are small in a population where virtually everyone is just as much a threat. But as Jessica Flanigan says, this does not entitle non-vaccinators “to harm others, even though the risk of harm is of low-probability, their victims are unlikely to identify them, and they do not intend to injure their victims” [16: 8]. Flanigan illustrates this point neatly with her comparison between not vaccinating and firing a gun into the air and thereby endangering innocent bystanders. The refusal to vaccinate, she claims, constitutes the same kind of potentially harmful reckless conduct, and exposes others to risk of harm in a morally analogous way [16: 7].

The obligation that we do not expose others to harm is further strengthened, we claim, by the increased numbers of those that we are exposing. Because most individuals are, by hypothesis, neglecting their obligation to vaccinate, there will be more of those who might be struck by our proverbial bullets of non-vaccination. The significance of non-vaccination risk is thus increased, it seems, as “the pool of people who are exposed to the risks of transmission becomes greater” [16: 12].12 If this is correct, and if our sense of obligation should track the numbers of those who we might endanger, then the moral obligation to vaccinate should become stronger the lower vaccination rates are. This explains why we might believe that there are specially placed individuals in society, like the staff in nursing homes [34: 326] and health care workers [2], who should have a particularly strong obligation to vaccinate due to the number of vulnerable people with whom they come into contact.

This is not to suggest that exposing a single vulnerable person to the risk of serious harm represents only a minimal moral transgression. We only contend that our moral sentiment seems rightly sensitive to the prospect of harming many, compared to the prospect of harming only a few. It would be morally negligent to shoot bullets into an area containing a single person, but it seems downright atrocious to open fire in a densely populated area. Still, both acts should be considered morally wrong.13

It could be argued that Flanigan’s gun-firing example does not accurately illustrate how individuals expose each other to the risk of harm when vaccination rates are low. If not being vaccinated is sufficient for individuals to be as negligent as those who free their guns into the air, then the circumstances of low vaccination rates are more akin to a gun-firing free-for-all, in which the majority of the population participates. Perhaps not vaccinating is indeed on a par with firing a gun into the air and exposing others to risk of harm, but these others expose us to risk of harm in the same way, and, assuming they have access to vaccination and are refusing it, should hardly be characterized as innocent bystanders. At the very least, they knowingly and willingly expose themselves to the risk of harm. Revising the gun-firing analogy in this way prompts two objections that bring our obligation well below the threshold into question.

First, what do we owe those who have knowingly and willingly placed themselves at risk of serious harm? While it seems beyond doubt that we must protect the vulnerable (those listed in the first section), others have become vulnerable of their own accord, and have, in addition, made themselves threats. Why should we have to undergo vaccination for their sake? Knowingly and willingly exposing oneself to harm of infection should, arguably, not add to the obligation set that others need to abide by to prevent that harm.

Still, this hardly seems sufficient to waive already existing obligations within that set, which certainly includes adopting low-cost measures of prevention. Imagine that a jaywalker is crossing the road that you are driving on. If you do not significantly reduce your speed, which is, presumably, within permitted limits, you will risk hitting the jaywalker and significantly harming him. Do you have an obligation to hit the brakes and reduce your speed? We believe most would share the intuition that you do. Note that carrying this obligation out even comes with a small risk to your safety (hitting the brakes could cause a serious traffic accident); yet, we believe the intuition that we are obliged to hit the brakes would persist.

It could be maintained that an obligation to adopt minimal measures of harm prevention does not translate into an obligation to vaccinate, since other less demanding measures could be taken to prevent the transmission of pathogens (like staying at home, maintaining a distance from others, or wearing a face mask). The controversial question is what constitutes this ‘bare minimum’ in harm prevention. Does it require less than vaccination? Supportive of vaccination as this bare minimum is the fact that, with many diseases, individuals could be asymptomatic carriers and represent viable threats without knowing it. Adopting other measures might only be sufficient to prevent harm if they are undertaken most of the time.

Second, in a gun-firing free-for-all, any person could be harmed by any number of shooters. In circumstances of low vaccination rates, it could be argued that my vaccination will prevent me from infecting another person, but will ultimately not make a significant difference to whether that person is infected. If persons are exposed to the extent that they will be infected anyway, the objection goes, then we should not be burdened by the obligation to vaccinate. Our knee-jerk reply to this objection is that such predictive certainty is unconvincing in considerations of public health and all individuals. But let’s imagine for the sake of argument that the prediction holds water. Even then, some authors claim, not vaccinating would be wrongful. Jason Brennan has argued that we should abide by the ‘clean hands principle’, according to which there is a “moral obligation not to participate in collectively harmful activities”, even if the outcome is overdetermined [5: 40]. Brennan uses the example of a firing squad, in which:

A band of 10 sharpshooters is about to kill an innocent child. They have been trained to shoot in such a way that each shot will hit the child at the same time, and each shot would be fatal on its own. You can’t stop them from killing the child. They ask you if you’d like to join in and take the 11th shot [5: 40].

Brennan argues that joining in with the sharpshooters violates the clean hand principle. Unlike the harm-based arguments we have so far defended, this principle points to a wrongness that is not sensitive to vaccination rates or considerations of prevention on the population level. Still, the principle would be sensitive to the consideration that, well below the threshold, there is a great number of those exposed to the risk of harm. By not vaccinating, an individual could participate in the harm of many, thereby violating the clean hand principle for each exposed individual. Thus, if we are convinced by the clean hand's principle, the numbers of those susceptible to harm should still be a weighty consideration. Therefore, even if vaccination makes no difference to those around us (which is at best dubious as a general prediction), it could still constitute a violation of a moral rule that is more likely and frequently broken well below the herd immunity threshold.14

Let us take stock. In this and the previous section, we have presented the first two harm-based arguments for a moral obligation to vaccinate. Most importantly, we argued that the two arguments run in opposite directions in terms of the strength of the obligation that they establish, given the different levels of vaccination coverage. Whereas the herd immunity argument establishes that the obligation becomes stronger as we draw closer to the herd immunity threshold, but is somewhat weak well below the threshold, the argument that we do not harm others ourselves generates the strongest obligation at the lowest levels of vaccination coverage. The two arguments are appealed to at different levels of vaccination coverage, which is why both are required for a stable harm-based moral obligation to vaccinate. But is the obligation stable even beyond the herd immunity threshold? We turn to this in the following section.

The Obligation Above the Threshold

In the previous two sections, we have spelled out two arguments grounding an individual obligation to vaccinate when rates are close to the herd immunity threshold (on either side) and well below it. If individuals discharged this obligation up to the point of reaching herd immunity thresholds for all mentioned infectious diseases, an important milestone for public health would already be reached. But would the obligation for individuals persist if herd immunity is secured? As stated in the first section, many individuals will want to avoid vaccination for religious and other lifestyle beliefs. We claim that for considerations of feasibility, which are relevant in virtually any modern social setting, the obligation to vaccinate should persist. In claiming this, we rely strictly on harm-based considerations.

Accounts centered on harm have already been fagged, mainly by their proponents, for their problems with grounding the obligation to vaccinate once the good of herd immunity has been obtained. As we mentioned, Dawson argues against such an obligation because vaccinating above the herd immunity threshold produces no additional benefit to others since herd immunity will have already minimized potential risks of harm; in fact, individuals who vaccinate in these circumstances are exposed to unnecessary risk given vaccination’s possible adverse effects [12: 171–177]. In other words, why expose a person to the risk of vaccination if she is already protected by herd immunity? In a similar vein, Pierik believes that high vaccination rates might allow for exemptions from vaccination [28: 226].15 However, both Dawson and Pierik stress that there are important pragmatic reasons to maintain vaccination rates as high as possible. Here, we offer two of what we regard to be the main pragmatic reasons that lend support to maintaining the obligation to vaccinate above the threshold. These weighty reasons arise in circumstances that, we hold, are ubiquitous even in the most advanced, currently feasible public health settings.

Before turning to these reasons, we should note that arguments in favor of the obligation to vaccinate have also been forwarded on fairness-based accounts. Most recently, Alberto Giubilini has argued that any individual who can reasonably bear her fair share of the burden in realizing herd immunity must do so, regardless of the impact that her contribution makes on the collective outcome [18: 50]. Deciding not to contribute our part in fulfilling a collective obligation means treating other obligation holders unfairly [17: 555]. A purported strength of a fairness-based account is that it is supposedly more successful than a harm-based account at explaining why the obligation should persist beyond the herd immunity threshold. If individuals do not have medical reasons for non-vaccination but have failed to take up their reasonable share of the collective burden, then they are treating those who have contributed to the collective good of herd immunity unfairly, even if herd immunity has already been realized. Thus, the fairness-based account more easily accommodates the intuition that there is something wrong with freeriding on herd immunity. 

The soundness of this moral implication hardly seems controversial. Yet, our focus here remains on the harm-based rationale, for two reasons. We want to suggest that fairness considerations are either merely complementary to considerations of harm or merely secondary to them.

Let’s take each possibility in turn. As we will show in this section, on a harm-based account, individuals are advised to vaccinate above the herd immunity threshold as a final precaution against herd immunity breaking down and against individuals themselves exposing others to risk of serious harm. Insofar, as the argument for vaccinating above the threshold is supplementary to our two previous (and more foundational) arguments in favor of vaccination, in circumstances below and around the threshold. A fairness-based account, on the other hand, successfully justifies the obligation around and above the threshold but makes a much weaker case for it well below the threshold. If hardly anyone undergoes vaccination in a population, then it is hard to see why an individual would be treating others unfairly by not vaccinating. Giubilini et al. acknowledge that if a fairness-based obligation existed in such circumstances, such an obligation would be weak, “and indeed it would be the weaker, the higher the number of people around me who fail to make their contribution” [17: 558]. 

Thus, using fairness as a standalone principle runs into difficulties with getting the obligation to vaccinate off the ground when vaccination rates are extremely low. But Giubilini et al. add that fairness considerations can be replaced in such circumstances by considerations of harm since individuals would retain the obligation “to be vaccinated to minimize the risk of harming others” [17: 558]. Therefore, the fairness account fails at grounding the obligation below the threshold and requires an alternative justification to cover a particularly significant blind spot, for which harm-based considerations are particularly suitable. The harm-based account, on the other hand, establishes the moral obligation to vaccinate, based on the two arguments we have presented in the previous two sections, from low vaccination rates to at least the point of realizing herd immunity. In this sense, the fairness account may be merely complementary to considerations of harm, since the latter seems to be more foundational in establishing the obligation.

But the fairness complement is required, we believe, only if considerations of harm cannot by themselves justify the obligation to vaccinate in all circumstances, which this section will try to argue against. If harm can justify the obligation in all circumstances, then, we believe, fairness considerations, although sound, become merely secondary to them. Although the fairness argument successfully highlights the injustice of not doing your fair share and free-riding on the contributions of others, these contributions concern the establishment of herd immunity, the purpose of which is to minimize harm. Surely, individuals should care about not treating others unfairly, but a more pertinent consideration in matters of infection is whether others will be exposed to the risk of possibly deadly harm as a result of our inaction. Insofar, as long as harm can justify the obligation on all sides of the herd immunity threshold, it should be a sufficient and primary justification for the obligation to vaccinate. Giubilini himself states that this might be the limit of the fairness consideration: 

We can think of fairness as a subordinate or secondary goal of vaccination policies: we do not enforce vaccination policies to promote fairness, but once we decide to enforce vaccination policies to realize herd immunity and prevent harm, fairness does become one of the goals of these policies, because herd immunity should be realized fairly [18: 108; emphasis in original].

Let us now turn to the pragmatic reasons for vaccination above the threshold. They point to the feasibility constraints in establishing the conditions of minimal harm from infection and serve as a precaution by buttressing herd immunity. We will mention two such reasons here.

First, even in the most modern public health settings, vaccination rates are prone to changes, which are often difficult to track in a timely and precise fashion. One aspect of the modern setting—population movements—arguably exacerbates these issues. Because individuals are now able to effortlessly travel from one country to another [17: 557], and change their place of residence much more easily than only a few decades ago, public health systems are facing greater challenges to make reliable estimations about vaccination coverage. 

For instance, in cities (like Dubrovnik) and countries that host a significant number of tourists, this will be a near-impossible task, at least during the tourist season. Attempting to protect the vulnerable may thus require even higher vaccination rates, under the precautionary assumption that the individuals coming into contact with the population are not vaccinated. In addition, individuals should be expected to vaccinate not only to protect the vulnerable members of their population but also of other populations, when they travel or migrate. There are, of course, further reasons why vaccination rates are sometimes unstable, and their monitoring unreliable. Fine et al. state that statistics may be inaccurate (or even falsified) and that vaccination is sometimes poorly administered or taken outside the recommended schedule [15: 914]. Or consider that vaccination rates have a standard tendency to drop, potentially below herd immunity levels, when children are born and vaccinated persons die.

The non-vaccinated person may thus face epistemic problems if she is attempting to assess the strength of her obligation by looking at immediate vaccination rates. These rates are both sufficiently unstable, and their tracking is too delayed for individuals to make informed assessments about the exact strength of their obligations. Recall that for most of these infectious diseases, herd immunity thresholds are over 90%, and it may represent a significant difference in the obligations of individuals whether the rates are one or two percentage points up or down. Because reliable information is often unavailable, individuals ought to vaccinate as a matter of precaution.16

Second, we mentioned earlier that herd immunity estimations are made under the assumption of a “homogenously mixed” population. This assumption is often unwarranted, due to “age-related, genetic, geographical, social, and behavioral factors” [1: 643]. Non-vaccinated individuals are often clustered together, for example, in schools and communities [29: 391], making them more vulnerable to outbreaks [15: 914]. These population clusters are particularly formed around shared religious beliefs, i.e., among individuals who are granted religious exemptions from vaccination ([14, 24]). Since these non-vaccinated individuals tend to interact with one another more so than with others, they find themselves at increased risk of harm [15: 914]. One recent finding strongly implicating this point concerns Jewish and Mennonite communities in New York, who accounted for over 75% of all measles cases in the US in 2019 [8]. When population clusters are present, the population might require a higher vaccination rate to be protected ([1: 643, 28: 228]). This effectively places a significant feasibility constraint on the normative possibility for individuals to reject vaccination on religious and lifestyle grounds above the threshold.

Holders of these religious beliefs might object that putting pressure on them to vaccinate is objectionably paternalistic to them and other members of their religious communities. As part of a population cluster, they primarily place those individuals at risk of harm who would be willing to accept such risks anyway. In addition, the content of their beliefs makes vaccination particularly costly to them, and their peers would never require them to compromise their way of life by vaccinating. In short, the idea is that pressuring the religious community into adopting the obligation to vaccinate, to minimize infection among them, disregards what members of this community consider to be good for them.

While it does seem reasonable for members of population clusters to agree to a greater risk of harm, they should not be permitted “to put their children at avoidable risk of death and suffering” [29: 382]. Children in population clusters (or at least a significant portion of them) cannot provide informed consent to risks of harm brought about by non-vaccination. Given that parents will not be able to avoid coming into potentially infectious contact with their children, these risks cannot be isolated only to those who would consent to them. Adults within the population clusters could argue that they will vaccinate their children while remaining unvaccinated themselves. This will indeed protect most children within the cluster, but some will remain at significant risk of infection. This is because some children are either too young to be vaccinated, or they belong to one of the two other vulnerable groups.17 Given the greater incidence of infectious disease in population clusters, vulnerable children will inescapably be exposed to considerable risks. An obligation to vaccinate should thus persist, even for adults within population clusters.

Finally, some authors have suggested that requirements for vaccination in a population could be arranged via a lottery ([5: 37, 28: 235]). The purpose of the lottery would be to provide exemptions for a small minority, but with an algorithm in place that would ensure homogeneity. Typically, we would conceive of such a suggestion to regulate mandatory vaccination, but it is not outside the realm of possibility for it to strictly coordinate our moral obligations to vaccinate. If such a lottery scheme were feasible, then the harm-based argument for vaccinating above the threshold would lose force, and our claim that the moral obligation is stable on both sides of the threshold would be compromised. However, the lottery proposal runs into its feasibility problems. 

For one, the lottery would have to be frequently repeated given the instability of vaccination rates that we described. Additionally, if the purpose of the lottery is only to help us assign a moral (and not a legal) obligation, the program would somehow have to compensate for the possibility of imperfect compliance. This would once again likely be accomplished by drawing fewer lots for exemption, thereby possibly assigning some obligations above the threshold. In short, the lottery proposal could establish some variance in assuming the obligation, but it remains to be seen whether this can be worked out in practice.18

Conclusion

In this paper, we offered three harm-based arguments in favor of a strong individual moral obligation to undergo vaccination. These arguments, we believe, show our obligation to be strong even when the population is well below or above a herd immunity threshold. First, we argued that individuals should participate in the collective effort of establishing herd immunity, thereby minimizing the spread of infection. Second, contrary to the claim that our obligation to vaccinate wears off when the population is well below the herd immunity threshold, we argued that it is strengthened the lower vaccination rates are, given the increased numbers of those who we might put in harm’s way through our infectiousness. 

Third, we provided pragmatic reasons for the claim that the moral obligation persists when the population has already established herd immunity, that is, once the population is well above the herd immunity threshold. These pragmatic reasons, we contend, are grounded in the feasibility constraints of establishing the conditions of minimal harm resulting from infections. Vaccination rates are difficult to track and are susceptible to changes due to population movements and shifting population demographics. Owing to the related epistemic issues about vaccination rates, the individual moral obligation to undergo vaccination persists in the form of a precautionary measure.

Acknowledgment

We would like to thank Abhishek Mishra, Aleksandar Simić, Luca Malatesta, Ivana Munitić, Tvrtko Jolić, Elvio Baccarini, and Peter Young for providing us with valuable feedback throughout the writing process. We also thank two anonymous reviewers for their useful comments.

Funding

Viktor Ivanković is supported by the Croatian Science Foundation (Grant Reference Number: HRZZ-UIP-2017-05-4308), as part of the ‘Harm, Intentions and Responsibility’ (HIRe) project. Lovro Savić is supported by Wellcome Trust. This research was funded in whole, or in part, by the Wellcome Trust [Grant number 212764/Z/18/Z]. For open access, the author has applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission.

Declarations

Conflict of interest The authors declare that they have no conflict of interest.

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