Press/Media Corner

Transmission of measles virus strain successfully interrupted in the Americas

Washington, DC, October 31, 2002 (PAHO) -- Measles is one of the most infectious diseases known to man and remains the leading cause of vaccine-preventable deaths worldwide, responsible for 590,000 deaths of children under 5 annually. Prior to introduction of the vaccine in 1963, practically all children became infected. In 1994, at the Pan American Sanitary Conference, Ministers of Health of the Americas embarked on the goal of interruption of indigenous measles transmission.


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The strategy recommended by the Pan American Health Organization (PAHO) for the interruption of measles transmission includes an initial mass vaccination campaign for children aged 9 months to 14 years and vaccination of children aged 12 months in routine vaccination services. This must be followed by complementary mass vaccination campaigns every four years for all children aged 1 to 4 years.

PAHO has recommended reaching 95 percent vaccination coverage in every municipality in every country. This strategy is complemented by a sensitive surveillance system capable of timely detecting suspected measles circulation, confirmation and thorough investigation of all cases, effective virologic surveillance, and strong supervision of vaccination activities, including house-to-house monitoring of vaccination coverage.

In the Americas, measles cases declined from approximately 250,000 in 1990 to 2,109 in 1996. But in 1997 there was a resurgence of measles virus circulation, with 52,284 confirmed cases reported from Brazil, which started with a large urban outbreak in São Paulo. The virus strain that caused the outbreak was D6, which had been circulating in Brazil (and possibly other countries of the region) since at least 1995. This outbreak spread to Argentina and Bolivia, where the largest number of measles cases occurred during 1998 and 1999, respectively, and then to Dominican Republic and Haiti, which had the largest number of cases in 2000 and 2001, respectively.

Sustained vaccination efforts by these countries led to the progressive decrease of cases region-wide to 3,209 in 1999 and 1,754 in 2000. In 2001, the total number of confirmed measles cases had dropped to 541, the lowest yearly number since the beginning of the hemispheric measles initiative. Since September 2001, no other viruses of the D6 strain have been identified in the Americas. Moreover, numerous countries with high measles vaccination coverage, including Brazil, Canada, Chile, Costa Rica, El Salvador, Chile, Mexico, Peru, United States and Uruguay, had measles case importations during 1999-2002 with limited or no secondary transmission.

In August 2001, a new measles outbreak began in Venezuela and spread to Colombia, after importation of the virus from Europe. The responsible virus was a new strain of measles, D9, never previously identified in the Americas. After both countries carried out significant vaccination campaigns, these outbreaks are being controlled. Through Oct.15, 2002, there were a total of 2,495 cases in Venezuela and 128 in Colombia. The last reported case occurred on September 20, 2002, in Venezuela.

By interrupting indigenous transmission of at least one indigenous measles strain, and by undergoing repeated measles importations with limited or no secondary transmission, countries of the Americas have shown that global measles eradication following PAHO's recommended strategies is possible.

Nonetheless, to maintain the Region free of indigenous measles transmission in the absence of global measles eradication, countries of the Americas will need vaccinate 95 percent of all children in all municipalities during each stage of the strategy, and sustain surveillance and case investigation efforts.

PAHO, which also serves as the Regional Office for the Americas of the World Health Organization, was established in 1902. PAHO Member States include all 35 countries in the Americas. France, the Kingdom of the Netherlands, and the United Kingdom of Great Britain and Northern Ireland are Participating States. PAHO is celebrating 100 years of work with all the countries of the Americas to improve the health and raise the living standards of their peoples.

For more information, please contact: Daniel Epstein, Office of Public Information, (202) 974-3459, e-mail:

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