To make an informed consent or refusal, individuals need a minimum level of capacity to receive information, understand it, make their choices and articulate them. However, each person is owed disclosure of information according to their own health literacy, which is further discussed in the next paragraph. In contrast to competency, which is determined by court, capacity is task specific—depends on a context [41]. Regarding vaccination, it is mostly parents who make decisions on behalf of their children, because the majority of vaccinations are scheduled in early childhood [41,50]. However, because a state also has a duty and interest in protecting a child from harm, it can challenge parental authority in situations in which a child is put at risk (the doctrine of parens patriae) [47]. The degree of parent’s autonomy depends on a type of planned intervention (or a type of vaccine); the higher a ratio between benefit and burden (having in mind the principles of beneficence and non-maleficence), the less decisive parents’ autonomy is, and vice versa (Figure 1). The role of parental autonomy is also affected by the principle of justice (in the context of vaccination, the need to contribute to the herd immunity in a population is its important part, which will be dealt with in the Discussion section).

For parental permission, adequate explanation which parents or their surrogates understand needs to be provided [47]. Lack of information, misunderstanding or false information are common causes for vaccine hesitancy or refusal [2,4]. Studies have shown that parents who delayed or refused vaccines do not consider the child’s health care provider as a reliable information source and are more likely to seek vaccine information on the Internet [2,30,51]. Prior to burdening parents with responsibility, which comes together with autonomy, it is the responsibility of accountable public health structures and its professionals and also of individual clinicians to provide adequate, reliable and understandable information about vaccination [52]. Improved parents’ education and their adequate informing play a key role in the promotion of vaccination and enable the parents to make responsible immunisation decisions [53,54,55]. Trust of the society in scientific evidence about vaccines, in the health care system and in vaccination policy is crucial, but not self-evident. It needs to be restored and maintained by provision of transparent information about vaccines, consistent attitudes of scientists and health care professionals and by the government taking responsibility for individuals affected by side effects [29,56]. Confidence is both a means and a result of ethically justified and efficient public health activities [56]. Additionally, a trustful relationship between medical personnel and parents is also important. Listening carefully to parent’s concerns and provision of clear information about risks and benefits of vaccination can help hesitant parents to understand principles of vaccination and, with their consent, to obviate ethical dilemmas of vaccine refusal [31,56]. However, because time meant for consultation with parents prior to vaccination is limited and it is often not possible to address all the parents’ concerns, a systematic approach is preferable (e.g., by social media or in organized forms of education about vaccination) [57].

A voluntary decision and absence of manipulation or coercion are an essential part of informed consent, though many factors may influence patient’s position (e.g., previous experience, social myths, opinion of family members and friends, clinician’s persuasion, legal obligations and constitutional pressures) [41,47]. Many of them do not threaten autonomous choice, even more, they are a fundamental part of decision making (so called “noncontrolling influence”) [41]. But some factors may limit one’s autonomy (“controlling influence”), and they also appear among reasons for vaccination hesitancy (i.e., conspiracy theories and family members’ pressure) [2,41]. These reasons need to be recognised and, if possible, avoided. A question arises, what is the relationship between autonomy and authority of behaviour prescribing organizations and traditions (i.e., government, religion, medical authority). Some claim that they are incompatible, but others see a conflict only when authority has not been properly delegated or accepted [41,58].

If all the above criteria for informed consent (or refusal) are met, parents can in some countries object to vaccination on personal, conscientious grounds (i.e., for religious, moral, or philosophical reasons (“non-medical exemptions”)) [3,41,51,59]. It is questionable if parents should be entitled to assert conscientious objection to vaccination, and, if so, what constraints this entitlement should be subject to [60,61]. Clarke et al. states that conscientious objection to vaccination for severe or highly contagious diseases is justified only in cases when the rate of its assertion does not threaten herd immunity [60]. In 2019 there were 45 states in the USA which allowed non-medical exemptions from immunisation [62]. Among European countries with mandatory vaccination policy, only two of them allowed non-medical exemptions in 2020 [63].

On the other hand, there also are physicians’ and other medical personnel’s autonomy [41,64,65]. It is exercised through right to refuse certain procedures or treatments on conscientious grounds. Because conscientious objection can contradict physician’s duties and may even limit patient’s access to health care, this right is subject to certain restrictions [64,66]. Some medical practitioners across the world refuse to treat children that are not vaccinated. Because this can affect access of unvaccinated children to health care, justification of applying conscientious objection in this case is debatable [67,68].

Though very safe, vaccines are not completely without risk [70]. Because they are usually administered to healthy children and are only potentially beneficial to them, any adverse event has a negative impact on the risk:benefit ratio [71,72]. The most of adverse events are mild (i.e., pain and swelling at the injection site, mild fever, rash or syncope) [71]. Anaphylactic reaction happens in approximately one per 1 million doses [70]. Some other rare severe adverse events are febrile seizures, immune thrombocytopenic purpura, disseminated varicella infection in varicella vaccine and intussusception in rotavirus vaccine [70,71,73]. Rarer adverse effects are mostly observed only after vaccine licensure, with continuous monitoring [71]. There are several independent bodies entitled for pursuance of this sensitive task; GACVS (Global Advisory Committee on Vaccine Safety) is based in Geneva and gives advice on vaccine safety to WHO, while two main programs in the U.S. are VAERS (Vaccine Adverse Event Reporting System), run by CDC and FDA, and Vaccine Safety Datalink (VSD) [71,74]. Because incorrect associations between certain vaccines and adverse effects were made in the past, a couple of myths have developed, which have fostered mistrust about vaccines [70]. A widely prevalent one is association between MMR vaccine and autism, which was rejected with strong evidence [70,75]. A solution to misconceptions about vaccines is providing reliable data on any possible adverse event and counselling parents about their concerns [71].

Although vaccines are appropriate for the vast majority of patients, there are particular groups which have a bigger risk to develop adverse events. By the principle of nonmaleficence, vaccination is contraindicated for them [71]. Contraindications can be temporary (i.e., current therapies (high dose steroids, chemotherapy …), pregnancy (for live attenuated vaccines) and reactivation of autoimmune disease) or permanent (i.e., allergy to vaccine’s ingredient, serious adverse events to a prior dose of vaccine and immunodeficiency (for live attenuated vaccines)) [71,76]. When there might be an increased risk for adverse effect, vaccination should be delayed or performed with caution in order to react properly [71]. Examples of precautions are a mild adverse event to a prior dose of vaccine and acute moderate to severe illness with or without fever [71,76]. Some conditions are wrongly perceived as contraindications (e.g., mild to moderate local reaction, current antimicrobial treatment, preterm birth and chronic diseases) [76]. Clear guidelines need to be accessible to everyone involved in vaccination in order to avoid such misconceptions and secure both safety and consistency in vaccination [7,76].

The principle of nonmaleficence needs to be applied also for a process of vaccine development and registration. Because this process is accompanied by uncertainties about possible adverse effects, a special attention needs to be paid in order to prevent harm to test subjects and future vaccine recipients [23,24,77,78]. Because children have limited capacity of understanding and may be subject to coercion, they are considered a vulnerable population [79]. Therefore, special attention and certain restrictions in trial design are needed in order to protect them [77,79]. On the other hand, children are owed optimal and novel treatment options, which makes clinical trials in the paediatric population unavoidable and essential [79,80].

Herd immunity has contributed to a dramatic decrease of infectious diseases or even to their eradication, and it has been clear that the benefit of immunisation strongly outweighs costs and risks [83]. But since in many countries’ vaccination programmes have been so successful, such that these diseases do not represent a direct risk anymore, the beneficial effect of vaccination has become less obvious [83]. When weighing risks and benefits of vaccination for an individual child in a population with low immunity rates or for non-communicable infectious diseases (e.g., tetanus and tick-borne meningoencephalitis), the benefits strongly outweigh risks [5]. On the other hand, when the level of herd immunity is high, vaccination of a single child has almost negligible beneficial effect for him or her [5]. However, because this is a result of an already established herd immunity, a risk:benefit analysis needs to include public health aspect (i.e., benefit for other individuals). Just contribution to benefits of vaccination is discussed in the following section.