[Vaccinations in childhood: when and why]

Community-based immunization is the primary method employed today to reduce the morbidity and mortality associated with the more common childhood viral and bacterial infections. Vaccines should be administered early in life so that the longest possible protection is offered. However the planning of vaccination programs must of course take into account the role of factors such as the immaturity of the neonatal immune system, passively acquired maternal antibodies, and the different epidemiologic and social situations. The authors discuss the epidemiology of viral and bacterial infections in infancy and the vaccination strategy to be followed for their prevention or eradication.