1.5.2 Vaccination

1.5.2.1 Mode of action and effectiveness of vaccination

Vaccination is the administration of small quantities of an attenuated or inactivated, basically pathogenic, micro-organism (bacteria or virus) or their fragments with the aim of protecting people or animals from the diseases caused by these micro-organisms as a precautionary measure. Vaccines are usually administered by subcutaneous or intramuscular injection, but there are also oral forms of administration. The action of vaccinations is based on two principles. First, the person receiving the vaccine develops an immune response against vaccine antigens. In classical vaccines, these antigens are actually in the injected fluid. In RNA, DNA and vector vaccines, these antigens are made by body cells of the person receiving the vaccine. Usually, IgM and IgG antibodies are produced as a result. In addition, specific T-memory cells develop, which will then remain present in lymph nodes or bone marrow for a long period of time. When the antigen next enters the body, it is either neutralised by the antibodies present in the blood or the activation of T-memory cells results in an accelerated, new production of IgG antibodies or other lymphocytes appear in the bloodstream to inactivate the microorganism. Thus, the vaccinated individual is first of all protected by the vaccination itself against the disease targeted by the vaccine.

Whether vaccination is effective depends largely on the so-called “vaccination coverage” in the population. If a significant proportion of the population is vaccinated against a particular disease, a bacterium or virus may be more difficult to spread among humans or animals. After all, in a vaccinated individual, a bacterium or virus is quickly rendered harmless by the circulating antibodies or the accelerated immune response. For further spread to other humans, it would have been necessary for the microorganism to have been able to multiply to some extent in the host, even if the host itself was not affected. After this multiplication, the microorganism would be transmitted to another individual via water droplets (spread via coughing or sneezing) or via blood or other body fluids (mucus, semen). After a successful vaccination, microorganisms do not manage to multiply or multiply less well in a host. A high vaccination rate therefore benefits others. These are of course those who have consciously decided not to be vaccinated, but also those who have not (yet) been vaccinated, those who are weakened by e.g. old age or illnesses associated with reduced immune defence or illnesses requiring treatment with immunosuppressive drugs. At what vaccination rate among the population the said protection of the unvaccinated occurs depends strictly on the disease. Nevertheless, the World Health Organisation (WHO) uses a target vaccination rate of 95% for almost all diseases for which vaccination is used. In the Netherlands, vaccination rates for DTP (diphtheria, tetanus and polio) and MMR (mumps, measles and rubella) had dropped to 90.0% and 90.1% respectively in 2017. [6: Rijksinstituut voor Volksgezondheid en Milieu. Vaccinatiegraad en jaarverslag Rijksvaccinatieprogramma Nederland 2017. Bilthoven 2018.]. In 2018, these values were 92.4 and 92.9%, respectively. [7: Rijksinstituut voor Volksgezondheid en Milieu. Vaccinatiegraad en jaarverslag Rijksvaccinatieprogramma Nederland 2018. Bilthoven 2019 doi:doi:10.21945/RIVM-2019-0015.] It is too early to conclude from this that the Netherlands is back on track to restore the required vaccination coverage.