Altered reactivity to measles virus in previously vaccinated children.

In children vaccinated with killed measles vaccine, exposure to natural rubeola within two to four years can result in a clinical syndrome of altered measles reactivity.During a small epidemic of measles in Edmonton, Alberta, 51 children who had received their last killed measles vaccination 27 to 45 months before, were admitted to hospital with this syndrome.The syndrome consists of a prodromal cough and high fever followed by a maculopapular rash appearing on the extremities and progressing centrally. Pulmonary consolidations with or without pleural effusions were evident, but these cleared rapidly in four or five days. Initial WBC and ESR values suggested a bacterial etiology, but no pathogens could be isolated.Complement fixation titres for rubeola are present in acute and convalescent sera and indicate a definite measles infection.Previous killed measles vaccination excites a delayed hypersensitivity which is activated by the natural measles infection to account for this syndrome.It is recommended that killed measles vaccine be no longer used in routine vaccinations.