1. Introduction

Vaccination is a key element in the contemporary health crisis due to the pandemic, since vaccines are one of the major «weapons» against COVID-19. However, vaccination rate is not enough to protect from the spread of the disease, both for voluntary and nonvoluntary reasons that prevent to achieve the so called «herd immunity». In this way, the problem of vaccination appears to have not only a medical, but also a deeply ethical dimension.

Indeed, on the one hand, some people are «anti-vaxxers» or «vaccine-hesitant», refusing to be inoculated; on the other hand, on a global level, entire populations of middle- and low- income countries (LMICs) cannot be vaccinated for reasons beyond their will, depending on economic, political and social factors. Actually, this is not a new problem, since vaccines have always faced similar challenges, but the contemporary health crisis has highlighted an unresolved problem on a global scale.

Starting from the analysis of the medical concept of herd immunity and obstacles to achieve it, the core assumption of this article is that the solution in response to the pandemic crisis ultimately lies in the acknowledgment and application of the principle of solidarity, both at an individual and at a national and international level. Moreover, the principle of solidarity implies the acknowledgment of the inherent relational nature of human beings, which grounds the dialectic between individual and common interest. Above all, it is evident the significance of the ethical perspective of Global Bioethics and the model on which it is based, namely the Universal Declaration on Bioethics and Human Rights (UDBHR), which challenges the mainstream approach.

2. The concept of herd immunity

The concept of herd immunity has a long history ⁽¹⁾. It was first used by some veterinarians in 1910 in relation to an epidemic of spontaneous miscarriage that affected cattle and sheep. In the 1920s, the bacteriologist Topley managed experimental epidemics in mice, observing that the prevalence of immune animals stopped the epidemic, and described it as «herd immunity», making a parallel with infectious diseases in children. Later, in 1924, the physician Doudley, recognizing Topley’s discoveries, applied the notion to humans, after having observed epidemics of diphtheria in a large group of students.

Nowadays, the concept is commonly used to indicate the indirect protection from infection conferred to susceptible individuals when sufficiently large proportion of immune individuals exist in a population⁽²⁾. Indeed, in a naive population a pathogen propagates affecting susceptible hosts. However, if a large group of people is immunized, the possibility of contact between infected individuals and susceptible hosts decreases. Two main parameters define the «seriousness» of the pandemic, particularly R («the average number of secondary infections caused by a single infectious individual introduced into a completely susceptible population») and R («the average number of secondary cases generated by a single index case over an infectious period in a partially immune population»).

There are two ways to achieve immunization: naturally, if the majority of population is infected; medically, trough vaccination. Herd immunity, in case of serious and mortal diseases such as COVID-19, cannot not be reached naturally, since many people would get sick and die and costs in terms of human lives would be very high ⁽¹⁾. Yet, immunity acquired through vaccines can last longer or shorter, conditioning the herd immunity threshold, which is «the point at which the portion of susceptible individuals falls below the threshold needed for transmission» ⁽²⁾.

The majority of vaccines gives a time-limited immunization and needs to be repeated ⁽²⁾. Since COVID-19 vaccines currently used produce a short duration of the protection and they do not seem to be transmission-blocking, almost all population should be vaccinated in order to guarantee the interruption of the transmission of the virus, thus protecting the most vulnerable individuals and the ones who cannot be inoculated for medical reasons ⁽³, ⁴⁾. For example, a level of herd immunity between 60 and 72% would be enough only if the vaccine provided life-long protection, otherwise the rate of vaccination should be higher ⁽³, ⁴⁾. Moreover, if vaccination is distributed irregularly, dangerous groups of susceptible hosts remain ⁽²⁾.

Starting from the above medical considerations, there are two ethically relevant obstacles to overcome in order to achieve herd immunity in the contemporary COVID-19 pandemic: the consistent number of people who voluntarily decide to refuse vaccines and entire populations of low- and middle-income countries that cannot access vaccines. Both issues need to be deepened.

3. The ethical perspective: autonomy vs. solidarity

Both vaccine hesitancy and the unfair distribution of vaccines on a global level call into question some ethical principles, emphasizing the opposition between individual liberty and collective benefit ⁽²⁴⁾. This conflict arises because the relational nature of the human being is not sufficiently recognized, especially in Western culture where individualism is the prevailing ideology and the individual is conceived as independent and autonomous from others, condemning any interference with the private sphere ⁽¹¹⁾.

Once acknowledged the concept of herd immunity and the need to increase vaccination rates, on an ethical level, despite psychological, cultural or religious constraints, the choice not to be inoculated reveals the preminence in the personal hierarchy of values of self-determination, although none of major ethical perspectives considers individual liberty an absolute value.

Indeed, according to the deontological approach, which is based on principles of universalizability, humanity and autonomy, personal beliefs can be disregarded in order to pursue common good.

The liberal perspective, although there are more views so that liberalism seems to fracture into a range of related but sometimes competing visions⁽²⁵⁾, recognizes that the individual has a primary role being holder of civil liberties, and that the state should respect subject’s freedom with a limited interference. Thus, even if it acknowledges more than any other philosophical perspective the principle of self-determination, liberalism also entails the need to restrict autonomy if it causes harms to other people. Therefore, some scholars, like Jason Brennan ⁽²⁶⁾, argue that even mandatory vaccination can be justified within the libertarian approach: Libertarians, and liberals in general, do not hold that all morally wrong actions may be coercively prohibited. Instead, they hold that we sometimes have the right to do wrong (...). However, libertarians (and liberals in general) hold that some moral duties are enforceable. The state cannot use coercion to make me let my parents visit their grandchildren, but it can coerce me into feeding my kids (...). Without here offering a full theory of why some duties are coercively enforceable and others not, I expect libertarians would hold that the state can use coercion to stop someone from actively spreading a dangerous disease. On this basis, Brennan endorses that, if a collective causes dangerous activities, the individual has the duty not to participate to them or withdraw, and he calls this obligation the «clean hands principle». Also principlism, that emphasizes four prima facie principles (beneficence, nonmaleficence, justice and autonomy), endorses that autonomy can be overcome if some specific conditions protecting competing principles are met ⁽²⁴⁾.

In addition, many contemporary authors, such as the Italian philosopher Alberto Giubilini, acknowledge the priority of social interest and common good over individual liberty in case of vaccination against communicable infectious diseases. In the book The ethics of vaccination, Giubilini supports that vaccination is an individual moral obligation -except in case of medical contraindications- and that the state has the moral responsibility to guarantee public health even trough obligatory vaccination. Indeed, ethics is, among other things, about whether and under what circumstances we should make choices that are not (only) in our self-interest but also or even primarily in the interest of other people⁽¹²⁾. As it has already been highlighted, in case of vaccines, especially the ones that induce relatively short-lived immunity like COVID-19 vaccination, the core question is achieving herd immunity, which holds both a medical and an ethical relevance rooted in the balance between individual and public interest. Thus, it requires the individual to make a choice for the sake of the public good, rather than exclusively for the sake of their own individual benefit⁽¹²⁾, calling for the contribution of every individual moral agent. However, the obligation to achieve herd immunity is not purely individual, since it also depends on collective, even if organized groups cannot be considered in the same way as individual agents from the moral point of view, being difficult to justify a collective responsibility ⁽¹²⁾. The solution is affirming the existence of an aggregate moral obligation, in which the collective have an obligation to realize herd immunity in the sense that the collective obligation is fulfilled trough the aggregate actions of collective members⁽¹²⁾. Indeed, a shared obligation generates individual obligations, since fairness requires the individual belonging to the community to take his or her own part of the weight of the total «burden» of vaccination ⁽¹²⁾.

Actually, individual interest conflicts with common good because of the adoption of an individualistic conception of autonomy. Yet, this is not the only possible interpretation. As Henk Ten Have ⁽¹¹⁾ wisely emphasizes, the opposition appears false when assuming the approach of global bioethics, since the first type of interests must be reinterpreted, while the last should be taken seriously. In other words, personal autonomy is ultimately a relational notion, because it originates and grows in an interpersonal and social context. Moreover, values are not simply individual but they are communicated into the society, being transmitted from generation to generation, thus human conduct is based on social rationality. Finally, autonomy and responsibility are linked, since individual actions affect other people life.

Likewise, the Italian Jesuit and professor of Moral Theology Father Carlo Casalone ⁽²⁷⁾ underlines a corresponding conception of autonomy. He supports that it is commonly conceived in a defensive way, as a means to protect the individual from the intrusion of political, religious or medical power, thus self-determination means full disposition of one’s life. However, the human person is crossed and constituted by relationships, receiving life from someone else and experiencing from the beginning to be placed in a context of relationships. Thus, Casalone concludes that this does not mean returning to paternalism but to introduce a not absolute, but relational and responsible, interpretation of autonomy.

The acknowledgment of the inherent relational nature of the human being is the foundation of the principle of solidarity, which is intrinsically connected to the principles of cooperation, responsibility and respect of vulnerability, not only because vulnerable individuals need solidarity, but also because the condition of vulnerability ontologically belongs to every human being ⁽²⁸⁾.

4. Solidarity and law

The most important legal document acknowledging the principle of solidarity is the UDBHR, which is the Magna Charta of global bioethics and of the bioethical approach based on human rights ⁽²⁴⁾. Although it is not a binding legal text, the Declaration clearly endorses the principle of solidarity, which is affirmed together with the principle of cooperation: Solidarity among human beings and international cooperation towards that end are to be encouraged (article 13). Particularly, it is the first document that formally included the principle of cooperation in bioethics, establishing a link with the concept of solidarity. Actually, this connection is extremely interesting, since it emphasizes that solidarity is not simply an individual action or a personal virtue, but it requires a social commitment ⁽²⁹⁾.

Even if it is not explicitly mentioned, also article 21 indirectly highlights the importance of solidarity and cooperation, especially when it affirms that transnational health research should be responsive to the needs of host countries, and the importance of research contributing to the alleviation of urgent global health problems should be recognized.

Likewise, article 24 recognizes both solidarity and cooperation. Indeed, first, it affirms that states should foster international dissemination of scientific information and encourage the free flow and sharing of scientific and technological knowledge; second they should promote cultural and scientific cooperation and enter into bilateral and multilateral agreements enabling developing countries to build up their capacity to participate in generating and sharing scientific knowledge, the related know-how and the benefits thereof; third, they should respect and promote solidarity between and among States, as well as individuals, families, groups and communities, with special regard for those rendered vulnerable by disease or disability or other personal, societal or environmental conditions and those with the most limited resources⁽²⁹⁾.

Moreover, as a corollary of the principle of solidarity, the UDBHR states the need to protect vulnerable people: In applying and advancing scientific knowledge, medical practice and associated technologies, human vulnerability should be taken into account. Individuals and groups of special vulnerability should be protected and the personal integrity of such individuals respected (article 8).

On a national level, the Italian working group Un diritto gentile⁽³⁴⁾, wrote a noteworthy document that recalls fundamental rights at stake in COVID-19 vaccination. It focuses on vaccination policies, and specifies conditions for COVID-19 compulsory vaccination. After having highlighted fundamental values of human coexistence rooted in every democratic system (dignity, freedom, equality, individual and public health, solidarity), the group acknowledges the need to balance individual and collective rights. In some circumstances, limiting individual freedom in the name of public health is possible, if and only if the sacrifice is proportionated, according to the Italian Constitution, which states that the Republic safeguards health as a fundamental right of the individual and as a collective interest (article 32). Thus, the imposition of compulsory vaccination is legitimate -with the exception of individuals with medical contraindications-, if and in so far as it is proposed as a measure proportionate in front of the seriousness of risks arising from the development of the pandemic in the global context. Moreover, the document recalls the need for international solidarity especially giving low-income countries the access to vaccines by distributing them according to compulsory licenses. Indeed, article 31 of the TRIPS agreement (Agreement on Trade-related Aspects of Intellectual Property Rights), which was specified by article 31 bis, identifies conditions required for obliging the holder of the monopoly to grant nonexclusive use to the state or other entities in the case of a national emergency or other circumstances of extreme urgency or in cases of public noncommercial use (article 31, b).

5. Conclusion

The standing point of this work is the medical analysis of the concept of herd immunity, which has not only a scientific value but also a moral dimension. Indeed, obstacles that prevent to achieve the herd immunity and thus to stop pandemic trough vaccines, both on an individual and on an international level eventually reveal the lack of solidarity and cooperation, along with the misconception of the principle of the respect of vulnerability.

However, the pandemic is teaching us that getting out of bonds of solidarity means not only harming other people but also self destruction, since the relational nature is a fundamental anthropological dimension, implying the true correspondence between humanity and relationality, although mutual dependency also means being exposed to vulnerability ⁽¹¹⁾. As the Pontifical Academy for Life ⁽³⁵⁾ rightly highlights: Never have we been called on to become aware of the reciprocity that is at the basis of our life as much as we have during this terrible emergency. Realizing that every life is a life in common, together we make up life, and life comes from «the other». Above all, on a global level, we need to be conscious that the risk of a global epidemic requires, in the context of responsibility, the introduction of global coordination in health care systems», acknowledging that «the strength of the process is determined by its weakest link.

At the same time, the voluntary refusal of vaccination by people having the opportunity to be inoculated is a «luxury» that does not find justification on any ethical approach, not even the most liberal one that recognizes the duty not to harm other individuals ⁽¹²⁾. If many inner and outer conditioning can influence choices of a subject, it is essential to recognize that the one who acts morally is called to discern what is good from what is evil having as his horizon the good for himself as well as for others, overcoming its conditioning in the name of a greater goal. Indeed, especially in case of public health crises such as pandemics, the goal of vaccination is the protection of society as a whole, so that appeals to self-interest cannot be separated from concerns with the interests of others⁽¹¹⁾.

This rejection is even more morally serious considering that millions of people are deprived a priori of this possibility just for the lack of resources, due to unfair political, social and economic systems, along with the deficiency of solidarity and cooperation by wealthier states ⁽¹²⁾. To be honest, even in low-income countries such as Africa there has been vaccine hesitancy in some small parts of the population, as a result of misinformation and manipulation led by international anti-vaxxers groups risen in Western countries and penetrated in urban areas where there is a greater possibility to use social media ⁽³⁶⁾. Despite these limited exceptions due to globalization, considering the understandable hesitation of people long exploited, living in environmental and cultural systems far from the Western ones, and accustomed to seek answers in nature rather than in science, it seems evident that the major evil to fight is vaccine nationalism, at least in «blind» and «ugly» forms.

The contemporary ethical perspective most acknowledging the need for solidarity, along with principles of cooperation, responsibility and respect of vulnerability, is Global Bioethics, which is rooted in principles recognized by the Universal Declaration of Bioethics and Human Rights. As Henk Ten Have (28) wrote in the fundamental book Global Bioethics. An introduction, solidarity is an essential moral and legal principle since «each individual person is powerless in the face of global problems; but together they can have an impact». Thus, the notion demonstrates that human beings are primarily social beings. They (thus we) can only live and flourish among other people with whom they (we) are connected. Solidarity cannot be explained in the language of self-interest.

To understand how the principle of solidarity is foundational, just think that it can be read in a «biocentric» key, which refers to being in solidarity with all life and all forms of life, in tune with Jahr’s thought ⁽³⁷⁾.

Therefore, it should become an indispensable element of ethical discernment determining a different balance of interests at stake, together with the ones recognized by the mainstream bioethics such as beneficence, non-maleficence, justice and autonomy. Particularly, the acknowledgment of the principle of solidarity, becoming an «axis» of a constellation of other principles such as cooperation, responsibility, and respect of vulnerable people, would make it possible to overcome a reductionist and partial ethical view, which often sees the triumph of self-sufficiency ⁽³⁸⁾.

As the Pontifical Academy for Life ⁽³⁵⁾ has masterfully affirmed: We are part of humanity and humanity is part of us. We must accept this dependency and appreciate the responsibility that makes us participants and protagonists in it. There is no right that does not have a resultant corresponding duty: the coexistence of those who are free and equal is an exquisitely ethical question, not a technical one.