atypical measles syndrome (AMS), a form of measles (rubeola) reported in persons immunized with a killed measles vaccine used in the United States from 1962 to 1967 and in Canada until 1970. Immunization with inactivated measles virus does not provide immunity and can sensitize the patient to the virus, resulting in an alteration of the disease. Symptoms differ from those of typical measles, beginning with a sudden high fever, headache, abdominal pain, and coughing. The measles rash may appear only 1 or 2 days later, usually starting on the hands and feet, rather than the head and neck. The infection may be complicated by edema of the extremities and pneumonia and may persist for up to 3 months.
