May 1997
---
Twenty-five percent of measles cases occurred in children
younger than 5.
ATLANTA — International importations and inadequate immunization are suspected as primary sources for the 488 confirmed cases of measles that occurred in 1996, according to a report issued by the Centers for Disease Control and Prevention (CDC).
Transmission occurred in school settings in seven outbreaks, accounting for 55% of all cases reported in 1996, and six outbreaks were associated with international importations, according to a CDC report.
Twenty-three measles outbreaks were reported by 15 states in 1996, accounting for 76% of the cases. The number of cases associated with outbreaks ranged from three to 121 (median: five cases), the CDC report said.
![[bar]](/art/gradred.gif){kind=small}
In four outbreaks, cases among school-age children occurred primarily in those who received only one dose of measles vaccine; in two outbreaks, cases occurred in school-age children who have religious or philosophic exemptions to vaccination. In Hawaii, an outbreak occurred in a college without a prematriculation vaccination requirement.
In cases related to vaccine failure among school-age children, the age distribution of cases reflected the type of second-dose policy implemented in the state. For example, Utah had the largest outbreak in 1996 and the requirement for a second dose of measles-mumps-rubella (MMR) vaccine at kindergarten entrance has existed since 1992; at the time of the outbreak, children age 5-9 years should have received a second dose of MMR.
Patterns of transmission of measles cases in 1996 highlight the importance of achieving high levels of second-dose coverage in all cohorts of school children as well as college students and assisting in global efforts to control measles, the CDC said.
To combat this problem, the Advisory Committee on Immunization Practices (ACIP) is revising its guidelines to recommend all school-age children receive a second dose of measles-containing vaccine by 2001. To limit the spread of measles transmission and to prevent future outbreaks during that interim, pediatricians should consider revaccinating school children in unaffected schools in counties where measles cases have occurred.
International importation was linked to six outbreaks. Genomic sequences from measles virus isolates from four outbreaks without an identified source case were similar to sequences from viruses identified as importations from Europe and Southeast Asia. This suggests that an additional 205 (42%) cases of the 488 provisional cases reported for 1996 were related to international importations.
International importations ac counted for 47 (10%) cases of measles and an additional 86 (18%) cases were epidemiologically linked to imported cases. None of the imported cases were acquired in countries in the Americas, according to the CDC.
Of the 465 measles patients for whom age was known, 117 (25%) were younger than 5 years old, including 37 younger than 12 months and 25 age 12-15 months. A total of 195 (42%) measles patients were 5 to 19 years old, and 153 (33%) were at least 20.
Vaccination status was reported in 354 patients, and varied by age group. All 32 patients younger than 1 year were unvaccinated, compared with 44 (71%) of 62 1- to 4-year-olds; 65 patients (48%) of 136 patients 5 to 19 years old and 85 (69%) of 124 patients at least 20.
Of the 77 patients for whom dates were available, 51 (66%) had received at least one dose of measles vaccine after their first birthday and 14 days before rash onset. Five cases of measles were reported among those who received two doses of measles vaccine after age 1, and one case was reported in a person who received three doses of measles vaccine.
Of the almost 500 provisional cases, 355 (73%) were indigenous to the United States, including 332 (68%) cases acquired in the state reporting the case and 23 (5%) cases resulting from spread from another state.
The strategy to eliminate indigenous transmission of measles in the United States includes: achieving high population immunity among both preschool children (with one dose of MMR) and school-age children (with two doses of MMR); improving the sensitivity of surveillance for and increasing laboratory confirmation of measles cases, rapidly implementing outbreak-control measures, and supporting international efforts to eliminate measles, according to the CDC.
For more information:
- CDC. Measles - United States, 1996, and the interruption of indigenous transmission. MMWR 1997;46:242-245.
You can express your
views on this article, or other relevant themes, in the
Infectious Diseases in Children
Specialty Forums.