Total elimination of measles in Finland.

On average, 15,000 cases of measles occurred annually in Finland before the initiation of a vaccination programme in 1975. Because of insufficient activity, the vaccination coverage failed to reach the required level of over 90%, and cases continued to occur. The policy was revolutionized in 1982 by launching a project in which the Schwarz strain was substituted by an attenuated Enders-Edmonston strain given as a component of a trivalent live-virus measles-mumps-rubella vaccine (MMRII). This vaccine is given twice, at the ages of 14-18 months and 6 years. The impact of the vaccinations has been monitored in several prospective studies. In addition to a very favourable safety profile, good immunogenicity and excellent clinical effectiveness have also been demonstrated. Since 1996 not a single case of measles has been found in Finland, although cases have been searched actively and serological confirmation has been required. Total interruption of virus circulation has brought a new problem: the possibility of vaccinees to acquire natural boosters is so rare that waning immunity has become a reality. As there is a continuous risk of measles originating from a foreign source, the only tool against an outbreak is to maintain a high vaccination coverage and to continue the two-dose schedule as a minimum policy.