The immunization status of children in an HMO

The immunization status of children within a well established Health Maintenance Organization is compared to data from 1973 and 1977 national surveys. The 1977 HMO data derive from a mail questionnaire survey and the 1973 data from the medical records. The HMO children are at less risk of diphtheria, pertussis, tetanus, polio, and measles while the opposite was true for rubella and mumps. The latter findings are related to earlier HMO policy, now modified.