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Public Health Dispatch: Absence of Transmission of the d9 Measles Virus
--- Region of the Americas, November 2002--March 2003
In 1994, countries of the Region of the Americas set a goal of interrupting indigenous measles transmission
(1), and the regional plan of action for achieving this goal was begun in 1996. As of March 16, 2003, the Region of the Americas has
been free for 17 weeks from known circulation of the d9* measles virus, the strain responsible for the only large outbreak of
measles in the region during 2002 (Figure).
The measles vaccination strategy recommended by the Pan American Health Organization (PAHO) includes a
one-time, national "catch-up" campaign for all children aged 1--14 years, routine "keep-up" vaccination for infants aged 1 year,
and national "follow-up" campaigns every 3--4 years for all children aged 1--4 years, regardless of measles vaccination history
(2). Other key components of the strategy include rapid house-to-house monitoring for local validation of vaccination activities and active epidemiologic and virologic surveillance
(3).
During 1997--2001, reported confirmed measles cases in the Region of the Americas decreased 99%, from 53,683 in
1997 to 541 in 2001 (4--6). During September 2001, transmission of the D6 measles virus genotype, which had circulated in
the
region since 1995 and had caused large outbreaks in Argentina, Bolivia, Brazil, the Dominican Republic, and Haiti,
was finally interrupted. However, also during September 2001, the recently discovered measles genotype d9 was introduced
into Venezuela by a Venezuelan traveler returning from Europe and resulted in an outbreak that spread to neighboring
Colombia during January 2002. This outbreak was attributable to low routine vaccination coverage in Venezuela
(7). Because Colombia, unlike Venezuela, did not have a large cohort of susceptible children, the outbreak was controlled easily. Following nationwide vaccination efforts by both countries, transmission of the d9 measles virus has been interrupted. The last reported
case occurred in Carabobo, Venezuela, on November 16, 2002. During the outbreak, 2,501 cases were reported in Venezuela and 140 in Colombia. As of March 16, no circulation of the d9 measles virus has been reported anywhere in the region for the preceding 17 weeks. During this same 17-week period, 1,066 suspected cases of measles were reported, of which 846 (79%) were measles IgM-antibody negative and discarded, 216 (20%) are still under
investigation but do not appear to be linked to a measles outbreak; four (<1%) were confirmed, one from Canada and three from the United States. These confirmed cases are presumed to be associated with importations; virus genotyping data are pending.
Progress toward interruption of indigenous measles transmission in the Region of the Americas reflects sustained
high political commitment by member countries and full implementation of PAHO's recommended measles-control strategies
and suggests that global measles eradication is achievable. However, important challenges remain. Measles is still endemic in
other regions, and sporadic cases continue to occur in the Region of the Americas because of importation. The majority of
countries in the region have not achieved and sustained routine measles vaccination coverage rates of
>95% in all municipalities. Because poor, underserved neighborhoods in large cities that attract migrants of rural origin are particularly at risk for measles outbreaks when the virus is reintroduced, persons living in these areas are targeted for supplementary vaccination activities.
Reported by:H Izurieta, MD, V Dietz, MD, P Carrasco, MPH, M Landaverde, MD, C Castillo, MD, Immunization Unit; M Brana, MPP, G Tambini, MD, Family and Community Health Area, Pan American Health Organization, Washington, DC. W Bellini, PhD, J Rota, MPH,
P Rota, PhD, Div of Viral and Rickettsial Diseases,
National Center for Infectious Diseases; F Lievano, MD, P Strebel, MD, Global
Immunization Div, National Immunization Program, CDC.
References
Pan American Health Organization. Elimination of measles in the Americas [Abstract]. Presented at the XXIV Meeting of the Pan American
Sanitary Conference. Washington, DC: Pan American Sanitary Conference, 1994.
de Quadros CA, Olivé JM, Hersh BS, et al. Measles elimination in the Americas---evolving strategies. JAMA 1996;275:224--9.
Izurieta H, Venczel L, Dietz V, et al. Monitoring measles eradication in the region of the Americas: critical activities and tools. J Infect Dis (in press).
Hersh BS, Tambini G, Nogueira AC, Carrasco P, de Quadros CA. Review of regional measles surveillance data in the Americas, 1996--1999.
Lancet 2000;355:1943--8.
*The lowercase letter is used for newly identified measles genotypes, pending an update of measles genotypes in the World Health Organization
Weekly Epidemiological Record.
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