The effect of a school entry law on mumps activity in a school district.

Sixty-three cases of clinical mumps occurring in a New Jersey school district presented an opportunity to determine compliance with the state's 1978 mumps "new entrants" school immunization law, investigate the effect of the law on the pattern of the outbreak, estimate the efficacy of mumps vaccine, and quantitate the economic impact of the outbreak. Only students in kindergarten (K) through grade 5 would have been affected by the immunization law. Students in the sixth grade were nearly seven times more likely to develop mumps than students in grades K through 5. The observed differences between the sixth graders and those in grades K through 5 most likely reflect the fact that sixth graders were not covered by the school law. Vaccine efficacy was estimated to be 91% (95% confidence interval = 77% to 93%). The total direct cost of the outbreak was $10,937 (clinic costs plus total cost to households). This outbreak demonstrates the significant impact of appropriate school vaccination laws on limiting the morbidity and economic and social costs of mumps.