WORLDWIDE MEASLES PREVENTION

Prior to measles vaccine use, measles accounted for over 2.5 million d eaths annually. Measles epidemiology in the developed countries is dif ferent from that in less developed countries. Whereas in the developin g world, measles is a disease primarily of young children, particularl y infants in urban areas, in the developed world, school-age children >5 years old play a greater role. Prevention of measles in developing countries has relied principally on a single dose of Schwarz strain va ccine at age 9 months (>85% efficacy); 80% coverage has prevented >1.6 million deaths. However, problems have been encountered because of th e narrow window to deliver vaccines between the time an infant becomes susceptible and exposure to disease. Recent studies suggest that some strains of measles vaccines given at potencies 10-100 times higher th an standard vaccines may achieve good efficacy in infants aged 4-6 mon ths, but safety of these vaccines has been questioned. Widespread use of standard vaccines in the West has resulted in dramatic reductions i n measles incidence but has not prevented outbreaks among the 2-5% of persons not protected by a single dose. Such outbreaks often appear af ter extended periods either without measles or with low measles incide nce. A single dose appears adequate to control measles well but inadeq uate to eliminate the disease. Many developed countries have adopted t wo-dose schedules. Measles immunization has dramatically reduced measl es occurrence, but improved control is necessary to prevent the estima ted 1 million deaths still occurring each year.