The Twelfth Technical Advisory Group Meeting on Vaccine Preventable-Diseases (TAG) of the Pan American Health Organization, was held in Guatemala, September 8-12, 1997. Formed in 1985 during the polio eradication campaign, the TAG meets every two years and functions as the leading forum to promote regional initiatives aimed at controlling and eliminating vaccine-preventable diseases. One of its main objectives has been to strengthen the policy dialogue on immunization among governments in the Region and participating agencies. The following are the TAG recommendations for measles:

Measles Eradication

Substantial progress has been made towards achieving the goal of measles elimination in the Americas. Transmission has been interrupted in many countries of the Region. The PAHO vaccination strategy (catch-up, keep-up and follow-up), where fully implemented, has proven to be highly effective. However, low levels of incidence can lead to a false sense of security. In the absence of measles transmission, susceptibles accumulate in a community, as a result of failure to vaccinate all children and because primary vaccination does not protect 5 to 10% of those vaccinated. These susceptibles can sustain future measles outbreaks. To maintain a measles-free state will require ongoing efforts to minimize susceptibility using the complete strategy.

The year 1996 was a notable year for the program with only 2109 confirmed cases of measles. However, in 1997, epidemic measles developed in Sao Paulo, Brazil with spread to other states in Brazil and at least four other countries of the Region. To date, over 4,000 laboratory confirmed cases of measles have been reported. At least two to three times that number may have occurred. Over one half of the cases occurred in unvaccinated persons 20-29 years of age. Several other countries have reported smaller but similar outbreaks in which substantial transmission appears to have occurred among adults.

The lack of a timely follow-up campaign and a deficient vaccination program appear to have been responsible, in part, for a rapid accumulation of susceptible children in Sao Paulo. Another contributing factor was the presence of many susceptible young adults due to migration from areas with low measles incidence, who would have not been targeted in follow-up campaigns. Epidemiological information about this outbreak is still incomplete. Little is known concerning the dynamics of measles transmission and risk factors for acquiring measles infection. A careful epidemiologic investigation is needed.

The Sao Paulo epidemic vividly illustrates the importance of all countries appreciating that the measles elimination effort is not a local or even a national campaign but a hemisphere-wide program which can only be as strong as its weakest component. This is true on a global scale as well because many cases in this Region have been linked either epidemiologically or virologically to importations from outside this hemisphere. Thus, better worldwide measles control is important to the continued success of measles elimination in the Americas.

General

• The occurrence of epidemic measles in a major urban area poses, by far, the most serious threat to the overall program because of the possibility of widespread disease dissemination. Accordingly, it is important that program success in all urban areas (population of >=1,000,000) be monitored on an ongoing basis by national authorities and reported to PAHO. The status of all cities should be published regularly and, for cities which are failing to sustain their efforts, special efforts should be made by national and international authorities to persuade responsible city officials of the need for corrective action.
• Over the next year and for the foreseeable future, surveillance throughout the Americas is critical in order to ascertain the extent and characterization of measles spread from the Sao Paulo epidemic. When measles is introduced, it is important to know the characteristics of individuals introducing infection and the characteristics of those acquiring infection. It is important to determine the likelihood of such outbreaks dying out with or without interventions. In particular, it is critical to evaluate whether adults are capable of sustaining transmission of measles over long periods when immunity levels are high among children. Only if such information is available, will it be possible to respond appropriately.

Vaccination Strategies

• Routine vaccination of infants (keep-up vaccination) is a critical component of the PAHO measles elimination strategy. To obtain a higher measles vaccine effectiveness, the age of routine vaccination should be increased from 9 months to 12 months of age. Once the age has been increased, coverage should be monitored among children 12-23 months of age. Efforts need to be made to vaccinate ³ 90% of infants at their first birthday in every district of every country. In countries with rubella/CRS control programs, MR or MMR vaccine should be used for routine infant vaccination.
• To maintain high population immunity among preschool-aged children, follow-up measles vaccination campaigns should be conducted whenever the estimated number of susceptible children 1-4 years of age approaches the number of children in one birth cohort. In countries with routine vaccination coverage in the 80-90% range, these campaigns should be conducted every 4 years. In these campaigns, all children 1-4 years of age should be vaccinated, regardless of previous vaccination or disease history status. Those countries with rubella/CRS control programs should use MR or MMR vaccine.
• High coverage for the follow-up campaigns is critical since in most countries they represent the last opportunity to provide measles vaccine to children who previously escaped vaccination. Immediately after these campaigns, the coverage in every district of the country should be determined. Those districts which did not achieve at least 90% of the target population should immediately conduct supplemental (mop-up) activities which may include door to door vaccination.
• The ultimate goal of the measles elimination effort is case prevention by reducing susceptibility through vaccination. The occurrence of cases represents a failure to anticipate disease risk and to take corrective action to prevent outbreaks. The most practical means for identifying susceptibility is to monitor coverage of routine immunization and immunization campaigns to estimate age-specific immunity levels. Serosurveys cannot be recommended for routine use because they often fail to detect the significant pockets of susceptibles who resist participating in surveys, they can be expensive, and they are methodologically difficult to perform and interpret.
• To assure high measles immunity among school-aged children, the vaccination status of all children entering school should be ascertained. Those students who are unable to provide documentation of prior measles vaccination should be vaccinated before being allowed to attend school.

Surveillance and Laboratory

• Measles surveillance is critical for ensuring progress towards the goal of measles elimination in the Americas. The purpose of measles surveillance is to detect virus circulation in a timely manner, to ascertain risk factors for measles, to obtain appropriate specimens for laboratory confirmation from suspected cases, and to provide information that will guide further prevention efforts.
• A standardized measles surveillance system is essential for monitoring progress toward the successful achievement of Region-wide measles elimination. All countries should provide the necessary data to the Region-wide measles elimination surveillance system (MESS).
• Communication and training efforts must be part of developing better surveillance systems. PAHO should support the development of training manuals, courses, and messages for use in the different countries of the Region.
• Each country should periodically evaluate the quality of its surveillance system. PAHO has developed a protocol for rapid evaluation of surveillance systems which should be disseminated to all countries of the region. A plan should be made for these evaluations in all countries as soon as possible.
• Laboratory confirmation is an essential part of the regional measles surveillance system. All isolated cases of measles and at least three cases from each chain of transmission should be confirmed by the laboratory. A single serum specimen collected at first contact with the health care system is sufficient for confirming measles.
• Suspected measles cases, with epidemiologic links to laboratory confirmed cases are themselves considered to be laboratory confirmed. Cases meeting the clinical case definition but which have neither laboratory confirmation nor epidemiologic links to a laboratory confirmed case represent failures of the surveillance system.
• Available data suggest that two commercially available measles IgM assays (Behring and Chemicon) are the most satisfactory tests for routine use. They are sensitive, specific and rapid (2-3 hours to perform). A positive result can be considered confirmatory of measles. Specimens that present special problems can still be sent to regional reference laboratories for confirmation by the CDC capture IgM assay.
• Virologic surveillance is important. Clinical specimens for viral isolation should be obtained from every chain of transmission. Urine, the most practical specimen to collect, should be obtained within 7 days of rash onset and forwarded to a laboratory to be properly processed. At present, virus isolation is performed at FIOCRUZ and CDC.

• If more than one birth cohort of susceptible preschool children has accumulated in an outbreak area, a mass campaign should be promptly conducted. All schoolchildren should be screened and all those who have not received at least one dose of vaccine should be vaccinated. All children presenting to a hospital emergency room or other health care facility during a measles outbreak should be vaccinated, regardless of prior vaccination status, provided there are no contraindications. During outbreaks, the routine age for measles vaccination should be lowered to 6 months.
• Countries should not implement indiscriminate campaigns to vaccinate all adults against measles. Most adults are likely to be immune and achieving significantly higher levels of coverage among adults is extremely difficult. However, where surveillance has identified specific risk groups for measles among adults, such as university students, health care workers, or others, targeted vaccination efforts may be useful.
• When importations are detected, countries should notify the country or countries where infection is likely to have been acquired. PAHO should facilitate cross country notifications.

Management Indicators

The following indicators are essential for monitoring the performance of the program:

³ 80% of reporting sites report on a weekly basis the presence or absence of suspected measles cases.

³ 80% of reporting sites report at least one suspected measles cases per year.

³ 80% of suspected measles cases are investigated within 48 hours of report.

³ 80% of suspected measles cases have a blood specimen collected if there is not an epidemiological link to a laboratory confirmed measles case.

³ 80% of measles chains of transmission have an identified source of infection.

³ 80% of specimens with results within 7 days of receipt in laboratory.