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Epidemiologic Notes and Reports Measles Outbreak -- Washington, 1989: Failure of Delayed Postexposure Prophylaxis with Vaccine

From March 1 through May 31, 1989, 19 confirmed measles cases* occurred in a health district in Washington (district attack rate: 26 cases per 100,000 population). No measles cases had been reported in the district since 1983. The index patient was an unvaccinated 3-year-old girl; five generations of cases followed.

Nine patients were less than 5 years of age, including five who were less than 16 months of age; eight were 5-19 years of age; and two were greater than 19 years of age. Eleven cases were in Hispanics (384 per 100,000 population**), and eight were in non-Hispanic whites (11 per 100,000**).

Three cases occurred in children vaccinated before the outbreak at greater than or equal to 15 months of age. Twelve patients had never been vaccinated; of these, five were less than 15 months of age, four had not received vaccine as recommended***, two had religious exemptions, and one was born before 1957.

Four cases were in children vaccinated during the outbreak. One child received vaccine 2 days after being exposed to measles on a school bus. The other three children were exposed to measles by their siblings. Assuming an incubation period of 14 days to onset of rash, these three children received vaccine 4, 5, and 7 days after they were infected.

Control measures included exclusion of students and teachers from school if they could not provide proof of immunity. Persons who were vaccinated within 72 hours after exposure or who had not been exposed to measles were immediately readmitted following vaccination. If vaccine was received greater than 72 hours after a well-defined community exposure, exclusion was continued for 14 days. Exclusion also was continued for 14 days for persons exposed at home and vaccinated greater than 72 hours after the start of the home contact's infectious period (defined as 4 days before rash onset).

Eight cases (42%) were epidemiologically linked to two of the three children vaccinated greater than 72 hours after infection. The child vaccinated 5 days after infection exposed six case-patients. Despite the exclusion policy, this child was in school when he developed prodromal symptoms 7 days after receiving vaccine. The child vaccinated 7 days after infection exposed two case-patients. This child attended church the day he developed prodromal symptoms, 4 days after vaccination. Reported by: P Malone, Chelan-Douglas Health District; B Baker, Immunization Program Office, JM Kobayashi, MD, State Epidemiologist, Washington Dept of Health. Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Measles vaccine may be protective when administered to susceptible persons after exposure, particularly if given within 72 hours (1-5). The Immunization Practices Advisory Committee (ACIP) recommends vaccination as the preferred prophylaxis in susceptible persons for up to 72 hours after measles exposure. Immune globulin is recommended by ACIP for selected persons (e.g., pregnant women and immunocompromised persons) and may modify or even prevent measles if administered between 72 hours and 6 days after exposure (6).

Although protection by vaccine is not absolute, the ACIP supports readmission to school of all previously unimmunized children immediately following vaccination. No distinction is made between children who are vaccinated within 72 hours of exposure and those whose vaccination is delayed. The more restrictive Washington policy that extends exclusion if children are not vaccinated within 72 hours of exposure is based on the diminished efficacy of delayed postexposure vaccination.

In the Washington outbreak, persons who received vaccine greater than 72 hours after exposure infected 42% of the case-patients, prolonging the outbreak substantially. The role that delayed postexposure vaccination may play in other measles outbreaks in the United States is unknown. During a more recent outbreak in this state, only one of 218 reported cases was in a child known to have been vaccinated greater than 72 hours after exposure (7).

Findings from this outbreak investigation illustrate the potential for measles transmission when postexposure vaccination is delayed and indicate a need to define the role of delayed postexposure vaccination in measles outbreaks in the United States. The disruption in education that would result from more restrictive national exclusion guidelines may offset the number of measles cases that might be prevented. New outbreak-control recommendations (6) calling for revaccination of all persons in at-risk schools who have not previously had two doses of vaccine should lessen the chances of spread from persons incubating measles at the time of vaccination.

References

  1. Sumner B, Starr S. Use of live-measles-vaccine to abort an expected outbreak of measles within a closed population. N Engl J Med 1963;269:75-7.

  2. Watson GI. Protection after exposure to measles by attenuated vaccine without gamma-globulin. Br Med J 1963;1:860-1.

  3. Fulginiti VA, Kempe CH. Measles exposure among vaccine recipients: response to measles exposure and antibody persistence among recipients of measles vaccine. Am J Dis Child 1963;106:450-61.

  4. Ruuskanen O, Salmi TT, Halonen P. Measles vaccination after exposure to natural measles. J Pediatr 1978;93:43-5.

  5. Addiss DG, Berg JL, Davis JP. Revaccination of previously vaccinated children with measles during an outbreak. J Infect Dis 1988;157:610-1.

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

  7. CDC. Measles--Washington, 1990. MMWR 1990;39:473-6. *Illness with generalized rash lasting greater than or equal to 3 days, temperature greater than or equal to 38.3 C (greater than or equal to 101 F), cough or coryza or conjunctivitis, and serologic confirmation or epidemiologic linkage to a serologically confirmed case. ** Based on 1988 population estimates. *** Vaccine is routinely indicated for persons born in or after 1957 who are greater than or equal to 15 months of age, lack evidence of immunity, have no medical contraindication to vaccination, and have no religious or philosophic exemption.

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