Measles - United States, 1986

A provisional total of 6,273 cases of measles in the United States was reported to the MMWR for 1986. This represents a 2.2-fold increase over the 2,822 cases reported in 1985, but is still 98% below the reported incidence in prevaccine years (Figure 1). The overall incidence rate increased from 1.2 cases per 100,000 population in 1985 to 2.7/100,000 in 1986. Nine states and New York City accounted for 4,941 (78.8%) of the cases: New York City reported 945; New Jersey, 911; Illinois, 710; California, 486; Texas, 397; Florida, 395; Wisconsin, 287; Arkansas, 278; South Carolina, 274; and Arizona, 258. Eleven states and New York City had incidence rates greater than 4/100,000 population: New York City had a rate of 13.4; New Jersey, 12.4; Arkansas, 12.2; Arizona, 9.3; South Carolina, 8.8; Wisconsin, 6.2; Illinois, 6.2; New Hampshire, 4.7; Iowa, 4.6; Washington, 4.3; Kansas 4.2; and Florida, 4.1. During 1986, 46 states and 347 (11.1%) of the 3,138 counties in the United States reported measles, compared with 38 states and 220 (7.0%) counties in 1985.

This report is based on detailed information reported to CDC's Division of Immunization on 6,255 of the provisional total of 6,273 cases for 1986. Of these, 96.9% met the standard case definition for measles *, and 34.2% were serologically confirmed. The usual seasonal pattern was observed, with the peak of the cases occurring in April (Figure 2). Otitis media was reported in 338 (5.4%) cases; pneumonia, in 152 (2.4%); and encephalitis, in 9 (0.1%). There were no deaths associated with measles.

One hundred and twenty-eight cases (2.0%) were known to be imported from other countries. An additional 123 (2.0%) cases were epidemiologically linked to imported cases within two generations of rash onset. There were 98 outbreaks (five or more epidemiologically related cases), accounting for 91.0% of all cases during 1986. Index cases were identified for 52 (53.1%) of outbreaks. Ten outbreaks with more than 100 cases each accounted for 58.8% of all reported cases.

In all age groups, the 1986 incidence rate was higher than the 1985 rate (Table 1) (1). The highest incidence rate in 1986 was reported among preschool-aged children<5 years of age (13.0 cases/100,000 population). Five states had outbreaks occurring predominantly among unvaccinated preschoolers. New Jersey had the highest incidence rate in preschoolers (108.9), followed by New York (56.4), Illinois (33.0) Florida (29.2), and Arizona (28.9). Of the total 2,454 preschool-aged children with measles, 692 (28.2%) were infants<1 year of age; 423 (17.2%) were 12-14 months of age; 114 (4.6%) were 15 months of age; and 1,225 (49.9%) were 16 months-4 years of age.

Of the 3,528 patients (56.4%) for whom the setting of transmission was reported, 1930 (547%) acquired measles in school (174 of these patients were on 21 college campuses); 689 (19.7%) acquired measles at home; 239 (6.8%), in medical settings; and 148 (4.2%), in day-care centers. The remaining cases were acquired in a variety of different settings, including churches, prisons, military training facilities, and the work place.

The vaccination status of patients in 1985 and 1986 was similar. Of the 6,255 patients reported for 1986, 39.3% had been appropriately vaccinated, including 992 (15.9%) who were vaccinated at 12-14 months of age and 1,466 (23.4%) who were vaccinated at >=15 months of age. A total of 3,509 (56.1%) measles patients were unvaccinated, and 288 (4.6%) had histories of inadequate vaccination (vaccinated before the first birthday).

Of the 6,255 cases, 2,278 (36.4%) were classified as preventable (Table 2) (2). However, there were striking age-specific differences among them. The highest proportion of preventable cases occurred among persons who were not of school age: 83.2% of cases among children 16 months-4 years of age were preventable, as were 72.2% of cases among persons 20-29 years of age. In contrast, 29.4% of cases among school-aged persons (5-19 years of age) were preventable.

Of the 3,977 nonpreventable cases, 1,230 (30.9%) were among persons too young for routine vaccination (<16 months of age), and 194 (5.0% were among persons too old (born before 1957); 2,377 (59.8%) had been vaccinated on or after their first birthday. Forty-eight cases (1.2%) occurred among foreign-born visitors to the United States. One hundred and twenty-eight (3.2%) patients had not been vaccinated because they either had medical contraindications or were exempt under state law (Table 3).

• Fever (38.3 C {101 F} or higher, if measured), generalized rash lasting 3 or more days, and at least one of the following: cough, coryza, or conjunctivitis.

Reported by: Div of Immunization, Center for Prevention Svcs CDC.

Editorial Note

Editorial Note: Since measles vaccine was licensed in 1963, the incidence of measles has declined to approximately 1%-2% of that reported in the prevaccine era (3). However, increases in the number of reported cases have occurred annually since the record low in 1983, when 1,497 cases were reported. There were more cases in 1986 than in any year since 1980, when 13,506 cases were reported (Figure 3).

In 1986, as in 1985, preschool-aged children had the highest reported incidence rate. Forty percent of all measles cases occurred among this age group in 1986. This high incidence was the result of several outbreaks which involved a substantial proportion of preschool-age children (4-6). These outbreaks occurred in densely populated, socioeconomically depressed urban areas. Immunization levels among preschoolers are known to be lower than those among school-aged children in many areas of the United States, and unvaccinated preschoolers were clustered in the areas where these outbreaks occurred. Large outbreaks also occurred among secondary school students in 1986, and they accounted for the increased incidence rate in this age group. A smaller proportion of reported cases occurred on college campuses than in previous years (1).

Although the number of measles cases reported in 1986 is still only about 2% of that in the prevaccine era, the increase in the number of cases in 1986 is of concern. There may be many reasons for this large increase; however, unvaccinated preschool-aged children and vaccine failures in school-aged children are two of the major ones.

Preventable cases are the result of a failure to fully implement the current measles elimination strategy. Unvaccinated preschoolers 16 months-4 years of age accounted for 44.7% of the total preventable cases in 1986. Preschool-aged children are difficult to reach because they are often not enrolled in institutions that require vaccination. Greater efforts need to be directed at increasing immunization levels in this age group. Complete implementation of the immunization requirements for measles prior to school entry, which exist in all states, should decrease the number of preventable measles cases in the school-aged population.

A substantial proportion of cases continue to occur in appropriately vaccinated individuals. A variety of different strategies have been suggested to decrease the number of these cases, including a routine 2-dose schedule and mass or selective revaccination either routinely or during an outbreak. Because only a small percentage of persons who were vaccinated at >= 12 months of age are susceptible and because identification of these susceptible persons is difficult, all of these strategies would result in administration of a large proportion of vaccine to persons who are already immune. Some studies have demonstrated lower vaccine efficacy and higher attack rates in persons vaccinated at 12-14 months of age (the recommended age for vaccination in the United States from 1965 to 1976 was 12 months of age) compared with those vaccinated at the currently recommended age of 15 months (7). While routine revaccination of persons vaccinated at 12-14 months of age is not recommended *, revaccination during selected outbreaks, particularly those in junior and senior high schools, may be considered (8).

While the continuing problem of measles in previously vaccinated persons suggests that additional strategies may be needed to eliminate measles from the United States, the present measles elimination strategy needs to be implemented more fully to decrease the number of preventable cases. Progress in measles control in other countries will also reduce the number of measles cases imported into the United States.

• Vaccination at 12 months of age is still highly effective (>80%).

References

1. CDC. Measles-United States, 1985. MMWR 1986;35:366-70.

2. CDC. Classification of measles cases and categorization of measles elimination programs. MMWR 198331:707-11.

3. CDC. Measles surveillance report no. 11, 1977-1981. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, 1982.

4. CDC. Measles-Arizona. MMWR 1986;35:99-100, 105-7.

5. CDC. Measles-New Jersey. MMWR 198635:213-5.

6. CDC. Measles-Dade County, Florida. MMWR 198736:45-8.

7. Orenstein WA, Markowitz L, Preblud SR, Hinman AR, Tomas A, Bart KJ. Appropriate age for measles vaccination in the United States. Dev Biol Stand 1986:65:13-21.

8. ACIP. Measles prevention. MMWR 1987 (In press).

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