Why get vaccinated?

The decision to vaccinate has two foundations: an individual one and one regarding the population as a whole.

From the individual point of view, in the presence of a vaccine-preventable disease that is relatively frequent, severe or fatal and in any case compromises personal well-being, it is clear that vaccination represents an advantage as long as the available vaccine products satisfy appropriate characteristics of efficacy and tolerability. For the vaccinations available and included in the vaccination schedule of our country, obviously all of these conditions are satisfied. The chance of getting the natural disease and its complications is significantly higher than that of suffering side effects caused by the vaccines themselves. Based on this simple principle, vaccinating is worthwhile.

However, for this simple logic to be applied, it is important to know precisely the likelihood of contracting a certain disease and its complications and to compare this with the probability of developing side effects caused by the vaccine. From the point of view of communication between doctor and patient, these data are often overlooked and the public find it difficult to gain a precise perception of the risk associated with the disease and that associated with vaccinations1.

An example of the assessment of the risks and benefits associated with vaccination is shown in Table 1 of the document “i rischi reali connessi alle vaccinazioni”]2.

A further dimension of the balance of the risks and benefits of vaccination concerns the benefits for populations. This aspect is applicable to diseases that are transmitted from person to person. For the latter the vaccination of population allows, once a sufficiently high and homogeneous vaccination coverage is reached, elimination and eradication of the diseases. In order to fulfil such an ambitious goal, vaccination strategies must be coordinated internationally. The advantage obtained from the eradication of a disease is obvious: when the conditions for the spread of and therefore the risk of infection no longer exist, the vaccination programme can be interrupted. Before reaching this goal, however, it is not possible to suspend vaccinations that aim to eradicate the disease, even when its frequency in a given geographical area is low or zero. The spread of pathogens in other geographical areas, in fact, represents a risk for the reintroduction of the disease even in areas where it has been absent for a long time due to the effect of vaccination programmes. Moreover, the frequent displacement of people allows the transmission of diseases at a great distance, in a capillary way, and in a short time, representing an extremely effective mode of diffusion3.

As is well-known, high vaccination coverage brings about ‘herd immunity’ for diseases transmitted from person to person4. This effect leads to the interruption of the spread of pathogens even if the vaccination coverage does not reach 100% and even if the vaccination efficacy is not 100%. It is obvious that these conditions will never be verified and in a vaccination programme there will always be individuals who cannot receive vaccinations because they have specific contraindications. These individuals, generally suffering from serious immunodeficiency diseases, are at high risk of infection and can develop more dangerous complications than healthy people, but they are indirectly protected by vaccination programmes when the coverage is such as to interrupt the spread of the pathogen.

Finally, there is an economic dimension to vaccination programs. This takes into account the direct and indirect expenses associated with the illness against the costs associated with vaccination strategies5.

These simple considerations have two practical implications. The conscious decision of the individual regarding vaccination that he or his children are to undertake, is based on the knowledge of current information about the clinical features and epidemiology of the disease, and the efficacy and safety characteristics of the vaccines. For this reason, any vaccination programme should be transparent for the public to "see first-hand" the current data and draw a clear balance between risks and benefits. A further consequence is that communication on these topics is crucial during routine medical examinations. An important role in this process is that of the trusted paediatrician who must devote appropriate time to the family to explain the details of the vaccination programmes.

While the decision-making process of the individual is based on a relatively simple budget, the decision to offer a vaccination from the point of view of public health can be quite complex6.

In a nutshell, the factors to be taken into consideration are the following:

  • Public health priorities
    Implementing a vaccination program and possibly introducing a new vaccination is an expensive operation both in financial terms and in terms of human resources. Even if all the countries of the world share a minimum vaccination program (Expanded Program on Immunization), the decision to offer a new vaccine depends strictly on the setting and the health situation of the individual countries. This explains, at least partially, the differences between the vaccination schedules observed worldwide.
  • Impact of the disease
    This is one of the fundamental aspects on which to decide the suitability of a vaccination offer. To estimate this impact, prevalence, incidence, hospitalisation, disability and mortality measures are used.
  • Effectiveness and safety of available vaccines
    These requirements are obviously essential for a vaccination programme to be justified. Given that the vaccines are administered to healthy people, mainly children, the standard of available products is very high in terms of efficacy, safety and tolerability.
  • Presence of other control strategies, including other vaccines
    For this aspect, too, it is important to establish the existence of alternative preventive strategies and to compare their effectiveness and other logistic aspects.
  • Economic and financial aspects
    Although vaccinations are a rare example of investment for health with a considerable economic return in terms of costs saved, there are not always sufficient resources to support vaccination programmes conducted by public health. In addition, vaccination programmes must be sustainable in the long term.
  • Logistical and programmatic aspects
    These aspects are often very relevant in developing countries. The introduction of a new vaccination program must consider the possibility of an appropriate management in terms of conservation and administration of the doses and availability of personnel for its management.

In summary, the decision to vaccinate, depends on precise factors that can be evaluated, in agreement with the doctor, by individual candidates for vaccination, and which is based on precise criteria in terms of public health. The assessment by the individual must permit the choice that involves the lowest risk, which is precisely to receive the vaccination when the preventable disease poses a concrete risk. For example, for a person who does not travel and does not go to an endemic area, it is not recommended (and not worthwhile) to vaccinate against yellow fever.

Table 1 - Effects of vaccine-preventable diseases, change in incidence associated with Canadian vaccination programme and adverse events associated with vaccination2

Disease Effects and Complications of disease Frequency pre-vaccination (Canada) Frequency post-vaccination) Vaccination collateral effects
Diphtheria Respiratory difficulty and failure, effects on the central nervous system, heart disease. Fatality 5-10%, higher in childhood and in the elderly. Average incidence 84.2 / 100,000, maximum annual peak over 9000 cases. Average incidence 0 / 100,000, maximum annual peak 1 case. For combined vaccines (penta and hexavalent) serious adverse events are rare. Common adverse events include a local reaction at the injection site, fever and irritability are less frequent.
Tetanus Generalised stiffness and convulsive spasms of skeletal musculature. Fatality above 10%, maximum risk in children and in the elderly. Average incidence 0.13 / 100,000, maximum annual peak 25 cases. Average incidence 0.01 / 100,000, maximum annual peak 8 cases. See above.
Pertussis Spasmodic cough, in newborns apnea, cyanosis, convulsions, pneumonia, sometimes death. Average incidence 156 / 100,000, maximum annual peak 19,878 cases. Average incidence 10.4 / 100,000, maximum annual peak 4,751 cases. See above.
Poliomyelitis Acute flaccid paralysis in about 1% of infections. Among the latter, fatality 5-10%. Average incidence 17.3 / 100,000, maximum annual peak 1,584 cases. Average incidence 0 / 100,000, maximum peak 0 cases. See above.
Hib nei bambini < 5 anni di età Meningitis in 55 to 65% of those infected, in other cases epiglottitis, bacteremia, cellulitis, pneumonia or septic arthritis. Fatality 5%, serious neurological sequelae in 10-15% and deafness in 15-20%. Average incidence 22.7 / 100,000, maximum annual peak 526 cases. Average incidence 0.9 / 100,000, maximum peak 17 cases. See above.
Morbillo Bronchopneumonia and otitis in about 10% of cases, encephalitis in 1/1000 cases (fatal in 15% and neurological sequelae in 25%). Rare subacute sclerosing panencephalitis. Thrombocytopenia 1/3000 cases. Fatality <0.05%. Average incidence 369.1 / 100,000, maximum annual peak 61,370 cases. Average incidence 0.2 / 100,000, maximum peak 199 cases. For the combined MPR vaccine fever and malaise in about 5%, up to 1% may develop a modest vaccine-related mumps, about 5% may have lymphadenomegaly or joint pain, more frequent in adult women. Transient thrombocytopenia in about 1 / 30,000 doses.
Parotite Serious complications are rare. In 20-30% of males in post-pubescent age orchitis. Deafness (usually 0.5-5 / 100,000 transient cases. Sometimes infertility and permanent deafness. Average incidence 248.9 / 100,000, maximum annual peak 43,671 cases. Average incidence 0.3 / 100,000, annual maximum peak 202 cases. See above.
Rosolia Encephalitis in 1/6000 cases. Infection during pregnancy causes congenital rubella syndrome. Average incidence 105.4 / 100,000, maximum annual peak 37,917 cases. Average incidence 0.1 / 100,000, maximum annual peak 29 cases. See above.
Sources / Bibliography
  1. Larson H, Brocard Paterson P, Erondu N. The globalization of risk and risk perception:
    Why we need a new model of risk communication for vaccines. Drug Saf. 2012;35:1053-9
  2. Public Agency of Health Canada. Comparison of effects of diseases and vaccine
  3. Alirol E, Getaz L, Stoll B, Chappuis F, Loutan L. Urbanisation and infectious diseases in a globalised world. Lancet Infect Dis. 2011;11:131-41
  4. Rashid H, Khandaker G, Booy R. Vaccination and herd immunity: what more do we know? Curr Opin Infect Dis. 2012;25:243-9
  5. Walker DG, Hutubessy R, Beutels P. WHO Guide for standardisation of economic evaluations of immunization programmes. Vaccine. 2010; 28:2356-9
  6. World Health Organization. Vaccine introduction guidelines. World Health Organization, 2005. IVB/0.5/18
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