Association between type 1 diabetes and Haemophilus influenzae type b vaccination: birth cohort study

Objectives To determine the effect of Haemophilus influenzae type b vaccina tion and its timing on the risk of type 1 diabetes in Finnish children. Design Cumulative incidence and relative risk of type 1 diabetes was compar ed among three birth cohorts of Finnish children: those born during the 24 months before the H influenzae type b vaccination trial, those in the trial cohort who were vaccinated at 3 months of age and later with a booster vac cine, and those in the trial cohort who were vaccinated at 24 months of age only. The probability of type 1 diabetes was estimated using regression an alysis assuming that there were no losses to 10 year follow up and no compe ting risks. Setting Finland (total population 5 million and annual birth rate 1.3%). Subjects 128 936 children born from 1 October 1983 to 1 September 1985, and 116 352 children born from 1 October 1985 to 31 August 1987. Main outcome measures Probability of type 1 diabetes among children vaccina ted with H influenzae type b and non-vaccinated children. Results No statistically significant difference was found at any time durin g the 10 year follow up in the risk of type 1 diabetes between the children born before the vaccination period and those vaccinated at the age of 24 m onths only (relative risk 1.01). The difference in the risk between the coh ort vaccinated first at the age of 3 months and the cohort vaccinated at th e age of 24 months only was not statistically significant either (1.06). Conclusion It is unlikely that H influenzae type b vaccination or its timin g cause type 1 diabetes in children.