Mass vaccination has been a successful public health strategy for many contagious diseases. The immunity of the vaccinated also protects others who cannot be safely or effectively vaccinated—including infants and the immunosuppressed. When vaccination rates fall, diseases like measles can rapidly resurge in a population. Those who cannot be vaccinated for medical reasons are at the highest risk of severe disease and death. They thus may bear the burden of others' freedom to opt out of vaccination. It is often asked whether it is legitimate for states to adopt and enforce mandatory universal vaccination. Yet this neglects a related question: are those who opt out, where it is permitted, morally responsible when others are harmed or die as a result of their decision? In this article, we argue that individuals who opt out of vaccination are morally responsible for resultant harms to others. Using measles as our main example, we demonstrate the ways in which opting out of vaccination can result in a significant risk of harm and death to others, especially infants and the immunosuppressed. We argue that imposing these risks without good justification is blameworthy and examine ways of reaching a coherent understanding of individual moral responsibility for harms in the context of the collective action required for disease transmission. Finally, we consider several objections to this view, provide counterarguments and suggest morally permissible alternatives to mandatory universal vaccination including controlled infection, self-imposed social isolation and financial penalties for refusal to vaccinate.The authors argue
Vaccine-preventable infectious diseases Many vaccine-preventable infections are transmitted between human beings and can cause serious harm or death. Measles, for example, is one of the most infectious known human viruses. It is transmitted via the airborne route, and outbreaks can result from minimal social contact between contagious and susceptible individuals. In most people, measles causes mild disease, but in some cases there are serious sequelae including lung inflammation (pneumonitis), brain inflammation (encephalitis), permanent disability and death. US historical data suggest a death rate of about 1 in every 350–1200 cases. Risks of both complications and death are highest in infants, young children, the malnourished and the immunosuppressed. Prior to widespread measles vaccination, there were, on average, 500 000 cases of measles and 400 deaths per year in the USA.1 Measles previously also accounted for a significant proportion of deaths among young people undergoing chemotherapy for leukaemia. Currently, measles continues to cause 100 000 deaths per year worldwide—mostly in children under 5 years of age in sub-Saharan Africa and India, in communities where vaccination rates remain suboptimal.
Modern inoculations for many common diseases are extremely safe and effectively prevent illness in the vast majority of those vaccinated. Vaccines have played a major role in the eradication of smallpox and near eradication of polio. High rates of vaccination against such diseases also protect those who cannot be safely vaccinated, such as infants and the immunosuppressed, through promotion of herd protection (or ‘herd immunity’). The measles vaccine is especially safe and effective, with significant side effects from vaccination being exceedingly rare. A careful long-term follow-up study of measles, mumps, and rubella (MMR) vaccination found zero deaths due to the vaccine and a less than one in a million chance of encephalitis.
There are several groups that cannot be safely or effectively vaccinated with some vaccines (eg, infants, the immunodeficient and the immunosuppressed). The only way these vulnerable individuals can be effectively protected against common infections, apart from extremely onerous social isolation (eg, ‘boy in a bubble’ scenarios), is through herd protection (achieved by high vaccination rates).ii Herd protection models for measles suggest that well over 90% of a population need to be vaccinated in order to reliably prevent sustained transmission. Recent outbreaks have shown that measles can spread quickly and cause significant harm when vaccination rates fall. The presence of such vulnerable individuals raises questions as to whether these people should bear the burdens of the decisions of others not to vaccinate and to what degree the latter should be considered morally responsible for resultant harms to the former.
In this article, we propose that those who opt out of vaccination are morally responsible (and in particular, blameworthy) for the harms suffered by others as a result of infectious outbreaks. In other words, non-vaccinators are morally blameworthy for the morbidity and mortality caused by infectious diseases that can be prevented by vaccination. Exactly how blame should in practice be apportioned among different individuals is a question that is beyond the scope of this article to resolve: but we show that there is at least one plausible and morally defensible way that blame could be ascribed to non-vaccinators. If our argument is sound, it joins other significant grounds that support public health intervention in this area.
We focus on the example of measles because it is highly contagious in social situations where people merely share the same air. Similar considerations apply to many other common infections transmitted in similar ways, but we leave aside diseases with other modes of transmission, noting that these differences and their moral aspects have received some attention elsewhere.
One way to support our thesis would be to analyse the concept of moral responsibility so as to identify sufficient conditions, and then to show that these conditions apply to non-vaccinators and the harms they cause. While we think this route is defensible, it is difficult to frame in a way that is not question-begging. Any account of sufficient conditions (for moral responsibility) that supports our conclusion is likely to be more contentious than the conclusion itself.
Instead, we adopt the following, two-pronged strategy. First, we simply conjecture that non-vaccinators are responsible for harms and present some relatively uncontentious necessary conditions of moral responsibility. We consider some possible objections to our responsibility thesis, organised around these conditions, and show that they all fail. Thus, we show that there is no knockdown objection to our claim. Second, we argue that there are a number of cases where we do in fact consider individuals blameworthy for harms that bear important similarities to the harms caused by non-vaccinators. The legitimacy of considering individuals responsible in these other cases suggests that it is analogously legitimate to consider non-vaccinators responsible.