Etiology of measles- and rubella-like illnesses in measles, mumps, and rubella-vaccinated children.

The viral etiology of measles- or rubella-like illnesses after MMR (measles, mumps, and rubella) vaccination was studied prospectively in 993 acutely ill Finnish children with fever and rash in 1983-1995. Their sera were tested for adeno-, entero-, and parvovirus B19 antibodies. Sera of 300 children <4 years old were also tested for human herpesvirus 6 (HHV-6) antibodies. Measles and rubella had been excluded by previous antibody testing. Serologic diagnosis of adeno-, entero-, or parvovirus infection was based on EIA (IgM or IgG antibodies) and that of HHV-6 on indirect immunofluorescence. A viral etiology was verified in 368 cases, most commonly parvovirus (20%), followed by enterovirus (9%) and adenovirus (4%). Among young children, HHV-6 infection was found in 37 (12%). Thirty-eight children (4%) had double infections. This study confirms that measles- or rubella-like illnesses in MMR-vaccinated children are often caused by other viruses. Each suspected vaccine failure requires laboratory confirmation to maintain reliable surveillance and control and to establish the specific etiology of the disease.