On March 3, 1989, the medical adviser of a private international school in Geneva telephoned the department of the Cantonal Medical Officer to report the occurrence of five cases of measles. The Geneva health services rapidly implemented prospective and retrospective surveillance that identified 12 other cases; in the subsequent 2-week period, nine new cases occurred, bringing the total to 26 cases among the 741 students at the school (Table 1).

The first case occurred during the week of January 11-17 (Figure 1) in a student from a central African country who had spent the Christmas holidays with his family. After report of the first cases, an information letter in English and French was sent to the parents, and a meeting was arranged at the school in preparation for an internal vaccination campaign. A series of articles on measles epidemics in communities were provided for the school nurse and made available to students and parents, and two vaccination sessions were organized at the school.

Students were not vaccinated if they submitted documentation of measles vaccination after the age of 15 months or a medical certificate stating that they had already had measles. Written authorization from their parents was required for their vaccination at the school. Boarders, whose parents generally could not be reached within the desired period, were vaccinated under the responsibility of the school.

Of the 255 students not already vaccinated against measles, 192 (26% of all students) were vaccinated during sessions organized at the school. The others were not vaccinated, either because they produced documentation of previous vaccination (198 (27%)); they were sick, absent, or had been vaccinated by a private physician when the epidemic occurred (63 (9%)); or the parents had not understood the information letter (288 (39%)) (in this case a second letter was sent). No new cases occurred after March 15.

For more than one third of the students, parents failed to reply with permission to vaccinate. Subsequently, the Youth Health Department sent recommendations to the school concerning the maintenance of students' medical records and the possibility of improved future collaboration.

Measles elimination will prove difficult in Switzerland because of the following constraints: 1) measles vaccination is not compulsory, 2) there is a shortage of data on vaccination coverage, 3) communicable diseases are not reported by practitioners, and 4) the structures capable of taking effective action in the event of an outbreak are inadequate. Adapted from the Weekly Epidemiological Record 1990;65:173-5. Based on a report by the Institute of Social and Preventive Medicine, University of Geneva. Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: This outbreak illustrates the potential for measles transmission in school settings, in particular when vaccination coverage is low. It is encouraging that health authorities in Switzerland took aggressive steps to try to control the outbreak. Low vaccination coverage among school-aged children was also felt to be a contributing factor during a recent communitywide outbreak of measles in Quebec (1).

Documentation of measles vaccination is not required for school attendees in Quebec (1) or Switzerland. Many students who lack documentation of vaccination probably receive measles vaccine as a result of routine childhood vaccination programs; however, lack of systematic vaccination in this population leads to accumulation of susceptibles, and measles outbreaks can occur. School vaccination requirements in the United States have been highly effective in increasing vaccine coverage among school-aged children and in decreasing the incidence of measles (2).

Outbreaks of measles in school settings can occur even with universal school vaccination requirements and high vaccination coverage. Some persons may remain susceptible as a result of exemptions to vaccination, and 2%-5% will be susceptible because of vaccine failure. In 1989, 170 measles outbreaks in the United States involving predominantly school-aged persons accounted for 32% of all reported cases. As many as 89% of patients in these outbreaks had been vaccinated on or after their first birthday (3). Routine administration of a second dose of measles vaccine will help to reduce the number of school-aged children who are susceptible because of vaccine failure and decrease the likelihood of outbreaks in this setting (4).

The outbreak-control strategy used during this school outbreak is not appropriate for measles control in the United States. Voluntary vaccination programs in schools may not successfully interrupt transmission (5). The Immunization Practices Advisory Committee (ACIP) recommends that during outbreaks of measles in schools and colleges all students who cannot provide documentation of measles immunity* be revaccinated with measles-mump-rubella vaccine (MMR) or be excluded from the setting (4). During the Geneva outbreak, no students were given second doses of measles vaccine. Furthermore, only 61% of students were either vaccinated or provided documentation of a single dose of vaccine. It is unclear whether the relatively low level of vaccine coverage influenced the course of the outbreak or whether the outbreak ended spontaneously.

Ensuring high immunity levels at the appropriate age is essential for prevention of measles transmission; other preventive measures include surveillance, reporting of suspected cases to health authorities, and prompt intervention to control outbreaks.

References

1. Anonymous. Update on measles in Quebec. Can Dis Weekly Rep 1989;147:15-29.

2. Robins KB, Brandling-Bennett D, Hinman AR. Low measles incidence: association with enforcement of school immunization laws. Am J Public Health 1981;71:270-4.

3. Gindler J, Atkinson WL, Markowitz LE, et al. Epidemiology of measles in the United States in 1989 (Abstract). In: Proceedings of the Epidemic Intelligence Service 39th Annual Conference. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1990:21.

4. CDC. Measles prevention: recommendations of the Immunzation Practices Advisory Committee (ACIP). MMWR 1989;38(no. S-9).

5. CDC. School exclusion in two measles outbreaks--Wisconsin. MMWR 1979;28:488,493-4.

*Physician-documented measles, born before 1957, serologic evidence of immunity, or documentation of two doses of measles vaccine on or after the first birthday.

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