Current Trends Measles -- United States, 1988

In 1988, a provisional total of 3411 measles cases was reported to the Division of Immunization, Center for Prevention Services, CDC, 7% less than the 3652 cases reported during the same period in 1987 (Figure 1) (1). The overall incidence rate for 1988 was 1.4 cases per 100,000 population. Nine states reported greater than or equal to 100 cases and accounted for 2802 (82.1%) cases: California (836), Pennsylvania (542), New Jersey (402), Texas (287), Virginia (239), Florida (170), Colorado (117), Ohio (109), and New Hampshire (100). Seven states had incidence rates greater than 2.0 per 100,000 population: Montana (10.7), New Hampshire (9.2), New Jersey (5.2), Pennsylvania (4.5), Virginia (4.0), Colorado (3.5), and California (3.0). Thirty-six states and 211 (6.7%) of the nation's 3138 counties reported measles cases.

A total of 3176 (93.1%) cases met the standard clinical case definition for measles,* and 1001 (29.3%) were serologically confirmed. The usual seasonal pattern was observed with cases peaking during weeks 18-25 (May and June).

Eighty-seven (2.6%) cases were known to be imported from other countries. An additional 126 (3.7%) cases were epidemiologically linked to imported cases within two generations. Fifty-seven outbreaks (five or more epidemiologically linked cases) were reported and accounted for 89.3% of all cases. Six outbreaks had greater than 100 cases and accounted for 52.7% of all reported cases. Most outbreaks occurred among school-aged children. The largest outbreak (611 cases) occurred in Los Angeles among unvaccinated preschool-aged children.

The incidence rate of measles decreased between 1987 and 1988 for 0-4-, 5-9-, and 10-14-year-olds, and increased in 15-19- and 20-24-year-olds. The highest incidence rate (5.8 per 100,000) occurred in 15-19-year-olds (Table 1).

Complications were reported in 408 (12.0%) cases. Otitis media was reported in 183 (5.4%); diarrhea, in 128 (3.8%); pneumonia, in 93 (2.7%); and encephalitis, in four (0.1%). Three hundred sixty-eight (10.8%) persons were hospitalized. Three measles-attributable deaths were reported (case-fatality rate: 0.9 deaths per 1000 cases).

Of the 2179 (63.9%) patients for whom setting of transmission was reported, 871 (40.0%) acquired measles in primary or secondary schools; 267 (12.3%), in colleges or universities; 553 (25.4%), at home; 127 (5.8%), in medical settings; 69 (3.2%), in day care; and 292 (13.4%), in a variety of other settings.

A total of 1548 (45.4%) patients had been vaccinated on or after the first birthday (Table 2), including 729 (21.4%) who were vaccinated at 12-14 months of age. One thousand eight hundred sixty-three (54.6%) persons were not vaccinated on or after the first birthday. Of these, vaccination would have been routinely indicated** for 803 (23.5%). Six hundred twenty-eight (18.4%) cases occurred in persons for whom vaccine was not routinely indicated, and 432 (12.7%) were unvaccinated for other reasons.

Of the 3411 reported cases, 1942 occurred among school-aged children. Of these, 1339 (68.9%) had been appropriately vaccinated. Most of the vaccine failures occurred in persons 12-19 years of age (Figure 2). Reported by: Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Since 1983, the number of reported measles cases increased annually until 1986, then decreased in 1987 and slightly in 1988 (Figure 1). In 1988, the age distribution of cases was similar to those in previous years. As in previous years, primarily two types of outbreaks occurred: those among highly vaccinated (vaccine coverage greater than 90%) school-aged children and those among unvaccinated preschool-aged children (2).

The epidemiology of measles points to two major impediments to measles elimination--unvaccinated preschool-aged children, allowing large outbreaks in inner-city areas, and vaccine failures, accounting for outbreaks in highly vaccinated school-aged populations. Therefore, in January 1989, the Immunization Practices Advisory Committee (ACIP) issued revised recommendations (3). First, ACIP lowered the age for routine measles vaccination in inner-city areas to as low as 9 months so that children would be vaccinated before they could be exposed to measles, and coverage would therefore be increased. Second, ACIP recommended that, for outbreaks in schools, previously vaccinated persons in specific target groups be revaccinated in affected schools and unaffected schools at risk for transmission. The groups targeted for revaccination are persons vaccinated before 1980 or vaccinated at 12-14 months of age. The rationale for choosing the 1980 date has been described (3). Data from four recent outbreak investigations have shown that persons vaccinated before 1980 are at increased risk for measles (Table 3). This is believed to be due primarily to a higher rate of failure of initial seroconversion for persons vaccinated before that time. Although children vaccinated between 12 and 14 months of age are at higher risk than are children vaccinated at older ages, only a minority of children with measles in most outbreaks have been vaccinated between these ages (1).

Implementation of these new outbreak-control recommendations during 1989 has been expensive because of the large number of outbreaks and cases. In the first 26 weeks of 1989, 8553 cases were reported, a 392% increase over the same period in 1988. More than 90 outbreaks have been reported; most have occurred in secondary schools and colleges. Seventy-one colleges have reported at least one case of measles. The largest outbreak has occurred in Houston, with greater than 1700 cases, primarily among unvaccinated preschool-aged children. Several states have spent several hundred thousand dollars each to revaccinate young adults in secondary schools and colleges.

Because of continued outbreaks among school-aged children, in May 1989, the ACIP decided to recommend a routine two-dose measles vaccination schedule. The second dose will be administered at entry to kindergarten or first grade (children 4-6 years of age). A two-dose schedule will decrease primary vaccine failures and thus the number of susceptibles and measles outbreaks in school-aged children. In addition, outbreak-control measures will be simplified. Detailed recommendations for this schedule and outbreak control are being formulated and will be published in the fall of 1989. Until then, the previously published schedules and recommendations should be followed. The American Academy of Pediatrics has also developed a routine two-dose measles vaccination schedule, which recommends that the second dose be given at entry to middle or junior high school (7).

The two-dose schedule will not affect outbreaks in inner-city areas among unvaccinated preschool-aged children. Prevention of such outbreaks requires intensive efforts directed at increasing age-appropriate immunization levels, which are being initiated by CDC and state and local health departments. These include activities in service delivery, assessment, information/education, operational research and surveillance. The two-dose schedule and intensive efforts to raise age-appropriate immunization levels should facilitate the goal of measles elimination in the United States.

References

1. CDC. Measles--United States, 1987. MMWR 1988;37:527-31.

2. Markowitz LE, Preblud SR, Orenstein WA, et al. Patterns of transmission in measles outbreaks in the United States, 1986-1987. N Engl J Med 1989;320:75-81.

3. ACIP. Measles prevention: supplementary statement. MMWR 1989;38:11-4.

4. Hutchins SS, Markowitz LE, Mead P, et al. A selective measles revaccination policy during a school-based measles outbreak (Abstract). In: CDC. Proceedings of the 1988 EIS Conference. Atlanta: US Department of Health and Human Services, Public Health Service, 1988:29.

5. Mast EE, Berg JL, Hanrahan LP, Davis JP. Measles in a highly vaccinated population: possible causes of measles vaccine failure (Abstract). In: CDC. Proceedings of the 1989 EIS Conference. Atlanta: US Department of Health and Human Services, Public Health Service, 1989:70.

6. Rullan JV, Pozo F, Gamble WB Jr, Jackson K, Parker RL. Measles in a highly vaccinated South Carolina school population (Abstract). In: CDC. Proceedings of the 1987 EIS Conference. Atlanta: US Department of Health and Human Services, Public Health Service, 1987:24.

7. American Academy of Pediatrics. Measles: reassessment of the current immunization policy. AAP News 1989;(July):6-7. *Fever greater than or equal to 101 F (greater than or equal to 38.3 C), if measured; generalized rash lasting greater than or equal to 3 days; and at least one of the following: cough, coryza, or conjunctivitis. **Cases in persons who were eligible for vaccination but who were not vaccinated.

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