The incidence of measles declined rapidly in Taiwan after the introduction of the measles vaccine Measles is a highly contagious disease with signifiinto the routine immunization schedule in 1978.
cant morbidity and mortality. Currently, measles con-However, an epidemic still occurred every 3-5 trol relies mainly on active immunization with a live, years until recently. A nationwide measlesattenuated vaccine. Previous studies suggested that we mumps-rubella (MMR) revaccination program may eliminate measles from a population by high vaccifor school and preschool children has been in
nation coverage [Krugman et al., 1963; Baba et al., place since 1992 Baba et al., place since to control the indigenous trans-1984]]. However, it has been noted recently that measles epidemics can occur even in a fully immunized popula-mission of measles. In order to understand the tion [Gustafson et al., 1987; Davis et al., 1987; Chen et current immune status after this recent national., 1989]. Regular use of measles vaccine has reduced wide revaccination program, we determined the dramatically the incidence of measles. Although more presence of measles IgG antibodies by enzymethan 50% of counties in the United States had remained linked immunosorbent assay (ELISA) in 1,281 free of measles for a decade or more, two main patterns blood samples from healthy persons aged from of measles transmission continued. First, outbreaks 2 months to above 30 years collected between continued to occur among highly vaccinated school-age 1993 and 1995, and also in another batch of 90 populations, in which measles transmission was docusera samples from children aged 2 years colmented among children who had received a single dose lected before 1992. The results showed that 1)
of vaccine [Gustafson et al., 1987]. The second pattern, the measles antibody seropositive rate (36.4%) as observed in the large epidemics of 1988-1991, was was lowest in children aged 5-7 months and rose transmission within unvaccinated ethnic and racial mito an unexpectedly high level of 85.8% at the age nority preschool children, particularly in the inner cities of 12-14 months, 2) the seropositive rate rose [Hersh et al., 1992]. A booster dose of MMR vaccine further to between 85.9% and 95.1% after 2 years before attending primary school or at 10-12 years old of age and remained high in adults and pregnant is currently suggested in the United States. This booster women, and 3) the seropositive rate of the 2is intended to increase overall vaccine coverage and to year-old children collected before 1992 was reduce primary and secondary vaccine failures. 61.4%, which was significantly lower than the In the prevaccination era, measles was an inevitable rate of the same age group collected after the disease before reaching adulthood , nationwide MMR revaccination program. We and there would be large-scale measles outbreaks every conclude that the national revaccination program 2 years in Taiwan. Measles vaccine was introduced to Taiwan in 1968. A mass immunization program with has promoted effectively measles immunity in one dose of vaccine for 9 to 36-month-old children was Taiwan. This immunity explains the rarity of reinstituted in Taipei city in 1977, and later for children ported measles cases since the last epidemic in aged 15-21 months throughout Taiwan in 1978. The 1989. This revaccination program should conpolicy reduced effectively measles mortality with only tinue and be extended to all preschool children one fatal case reported in 1983 [Department of Health, and young adults so that indigenous measles can be eliminated by the year 2000.