Current Trends Mumps -- United States, 1985-1988

After the introduction of live mumps virus vaccine in 1967 and the recommendation for its routine use in 1977, the incidence rate of reported mumps cases in the United States decreased steadily. In 1985, a record low of 2982 cases occurred, representing a 98.0% decline from the 152,000 cases reported in 1968 (Figure 1). However, from 1985 to 1987, mumps increased; 7790 and 12,848 cases were reported in 1986 and 1987, respectively. During this time, the annual reported incidence rate rose almost fivefold, from 1.1 cases/100,000 population to 5.2 cases/100,000 population (Table 1). However, in 1988, a provisional total of 4730 cases was reported, representing a 63.2% decrease from 1987.

In 1987, of the 48 areas (47 states plus the District of Columbia) that routinely reported mumps cases, at least one mumps case was reported from all but three (Delaware, Rhode Island, and Wyoming) of the reporting areas. Similarly, in 1988, all except Maine, North Dakota, and Rhode Island have provisionally reported mumps cases. In 1985, seven states (Illinois, Tennessee, Michigan, Wisconsin, Indiana, Louisiana, and Minnesota) reported more than 500 cases each (case range: 810-2737, incidence range: 18.1-37.7 cases/100,000 population). In addition, in 1985, 680 (22.8%) of the 2982 counties in the 48 reporting areas reported at least one case, compared with 889 (28.3%) of 3138 in 1987. During 1987, 31 (64.6%) of the 48 reporting areas noted more mumps cases than in 1986.

Final age-specific data are available through 1987 (Table 1). Most (55.2%) mumps cases reported in 1987 occurred in school-aged children (5-14 years of age). For comparison, an average of 74.6% of reported cases occurred in this age group between 1967 and 1971 (the first 5-year period postlicensure). However, whereas an annual average of 8.3% of reported cases were among persons greater than or equal to15 years of age in 1967-1971, this age group accounted for 38.3% of the reported total in 1987. Although reported mumps incidence increased in all age groups from 1985 to 1987, rates increased most substantially among 10-14-year-olds (almost a sevenfold increase) and 15-19-year-olds (over an eightfold increase) (Table 1). For the first time since mumps became a reportable disease, the reported peak incidence rate shifted for 2 consecutive years from 5-9-year-olds, the age group traditionally associated with the highest risk of disease (1,2), to older age groups. The increased occurrence of mumps in susceptible adolescents and young adults has been demonstrated in several recent outbreaks on college campuses (3) and in occupational settings (4). Nonetheless, despite this age shift in the epidemiology of reported mumps, the overall risk of disease in persons 10-14 and greater than or equal to15 years of age is still lower than that in the prevaccine and early postvaccine licensure periods.

Reported incidence rates continue to be affected by school immunization laws (5). For example, in the 15 areas (14 states and the District of Columbia) that had comprehensive (i.e., kindergarten through grade 12 (K-12)) laws requiring proof of immunity against mumps for school attendance, the incidence rate in 1987 was 1.1 mumps cases/100,000 population (Table 2). In contrast, mumps incidence was highest in the 14 states routinely reporting mumps cases in 1987 that had no requirements for mumps vaccination (11.5 cases/100,000 population) and intermediate (6.2 cases/100,000 population) in the 18 states with partial vaccination requirements for school attendance (i.e., those that include some children but do not comprehensively include K-12) that routinely reported cases. All states that had greater than 500 reported cases in 1987 had either no or partial school immunization requirements. Provisional 1988 data suggest this trend is continuing, with incidence rates of 1.4/100,000 in states with K-12 laws in effect at the beginning of that year, 1.9/100,000 in states with partial requirements in effect at the beginning of that year, and 3.2/100,000 in states with no school immunization laws in effect at the beginning of that year.

The shift in age-specific risk noted above occurred only in states without comprehensive K-12 school vaccination requirements. Mumps incidence in 1987 decreased substantially in preschool- and school-aged children, even in the absence of any school laws; however, the reported incidence rates for 10-14-year-olds in states with no laws (65.5 cases/100,000 population) approached 1967-1971 levels (75.5 cases/100,000 population) (Figure 2). For persons greater than or equal to15 years of age in such states, the reported rates were equivalent to reported 1967-1971 rates (both at 5.8 cases/100,000 population). Reported by: Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Through 1987, more than 82.3 million doses of live mumps virus vaccine were distributed in the United States. The principal strategy to control mumps in the United States is to achieve and maintain high immunization levels, primarily among infants and young children. The Immunization Practices Advisory Committee of the Public Health Service recommends that universal mumps immunization routinely should be carried out in physicians' offices and public health clinics in all communities; trivalent measles-mumps-rubella (MMR) vaccine is the vaccine formulation of choice (6). This strategy is also cost-effective (7,8). Unless otherwise contraindicated, all persons thought to be susceptible should be vaccinated. Susceptible persons include those without documentation of 1) physician-diagnosed mumps, 2) immunization with live mumps virus vaccine at greater than or equal to12 months of age, or 3) laboratory evidence of immunity.

Ensuring immunity for adolescents and young adults is especially important, given the recent shift in risk of disease to these age groups. This trend does not appear to be due to waning immunity in persons vaccinated previously and is probably attributable to the relatively underimmunized cohort of children born between 1967 and 1977 (9). The evidence that the shift in risk to older persons through 1987 is limited to states without comprehensive mumps immunization school laws provides further evidence that the relative resurgence of mumps in the United States is not due to vaccine failure but to a failure to vaccinate.

Although seroepidemiologic surveys, especially of adolescents and young adults, are needed to better define the magnitude and extent of susceptible cohorts, several actions are necessary to decrease the pool of susceptibles and to ensure that high rates of immunization are maintained. The adoption and enforcement of universal comprehensive vaccination requirements for school attendance are likely to reduce mumps incidence substantially. At the end of 1988, 17 states and the District of Columbia had comprehensive K-12 laws in effect, 18 states had partial vaccination requirements, and 15 states had no requirements for mumps vaccination (Figure 3). Tennessee and Illinois, which together accounted for 57% and 31% of the total number of reported U.S. mumps cases in 1986 and 1987, respectively, have recently enacted comprehensive K-12 requirements. Similar requirements in colleges, as recommended by the American College Health Association (10), and selected places of employment should also be considered; selected places of employment where persons in this age cohort are likely to be concentrated or where the consequences of disease spread may be more severe (e.g., medical-care settings) would help focus attention on groups that appear to be at highest risk. More aggressive outbreak control, including exclusion of susceptibles from school, is also helpful in eliminating transmission in mumps epidemics.

References

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