Immunisation strategies are various and their effect partially unpredictable. In Japan, the strategy
of immunising children to protect the elderly was effective, but the population did not accept
it. The implications of immunising against rubella in childhood or during the fertile age
are quite different. Early immunisation against measles has the consequence of reducing the
herd immunity in adult age. Variability of immunisation campaigns against diphtheria in Russia
and Poland produced an immunity gap, with consequent epidemics. The present immunisation
strategy against pertussis, which implies an higher infection risk in the adult age, may
also have to be revised.