DECLINE OF MUMPS ANTIBODIES IN TYPE-1 (INSULIN-DEPENDENT) DIABETIC CHILDREN AND A PLATEAU IN THE RISING INCIDENCE OF TYPE-1 DIABETES AFTER INTRODUCTION OF THE MUMPS-MEASLES-RUBELLA VACCINE IN FINLAND

A nationwide mumps-measles-rubella vaccination was introduced in 1982 in Finland to children aged 1.5 to 6 years and since then mumps has virtually disappeared in the country. We investigated whether this rapid epidemiological change had any impact on antibody activity against mumps virus in Type 1 (insulin-dependent) diabetic children or on the incidence of Type 1 diabetes in Finland. Two case-control series were collected before (series I and II) and three series after (series III-V) the introduction of the vaccination. IgA class mumps antibody levels were significantly higher in Type 1 diabetic children than in matched control children in the first two but not in the three later series. IgG class antibody levels were similar in patients and control subjects in the first two series but significantly lower in patients than in control subjects in the three later series. The overall incidence of Type 1 diabetes in 0-14-year-old children increased until 1987 but remained about the same during 1988-1990. In 5-9-year-old children no further increase in Type 1 diabetes was seen since 1985, whereas in 0-4-year-old children the incidence continued to rise until 1990. The results suggest that the elimination of natural mumps by mumps-measles-rubella vaccination may have decreased the risk for Type 1 diabetes in Finland; a possible causal relationship is substantiated by the observed concomitant decrease in mumps antibody levels in diabetic children. However, further studies are required to determine if the vaccine virus, like natural mumps, could trigger the clinical onset of Type 1 diabetes in young children.