Vaccination is considered to be the most effective and the cheapest medical intervention through which individual and collective immunisation is achieved. Statistics show that, at present, immunisation annually saves 400 million lives and protects approximately 750,000 children against disabilities of varying degrees. Approximately 80% of worldwide children are vaccinated against diphtheria, tetanus, pertussis, polio, measles, etc.; these diseases used to be considered incurable in the past. Vaccines help the body to produce antibodies; they help the immune system to detect germs and inactivate their cells. The immunological protection is installed after a variable period of time following the inoculation and is long lasting. Immunisations can be achieved in several ways: through national immunisation campaigns with general recommendation--they may be compulsory, optional or prophylactic (for the diseases for which a vaccine is available); vaccinations not included in the compulsory immunisation programmes; they may also be targeted to the contagious infectious outbreaks or to groups of population in certain situations. There is no guarantee that a vaccine will provide 100% protection. However, it will significantly reduce the risk of getting an infection. Vaccines have side effects which can be divided into reactions triggered by the vaccine or reactions exacerbated by it, without a causal relationship to the vaccine.