| Study characteristics |
| Methods |
Cohort study |
| Participants |
Danish birth cohorts 1990 to 2000. Children in the cohort were followed from birth until 31 December 2001, or until they received a diagnosis of type 1 diabetes, died, were lost to follow‐up or emigrated, or reached 12 years of age, whichever occurred first. A total of 739,694 children were included. |
| Interventions |
MMR (1990 through 2001), Denmark had a nationwide policy of vaccinating children against MMR. The dates of vaccination with the first, second, or third dose of the vaccines were obtained from the National Board of Health. In Denmark, childhood vaccinations are administered solely by general practitioners, who are reimbursed when they report these data to the National Board of Health. The National Board of Health has kept a register of these reports since 1990. Data on the MMR vaccine have been available only since September 1991, thus children born in 1990 were classified as having unknown MMR vaccine status. |
| Outcomes |
Type 1 diabetes:information on the diagnosis of type 1 diabetes from 1 January 1990 through 31 December 2001 was obtained from the Danish National Hospital Register. From 1990 through 1993, Denmark used a modified version of the International Classification of Diseases, 8th Revision (ICD‐8). From 1994 through 2001, the ICD‐10 was used. The authors used codes 249 and E10 (the code 249 does not exist in the standard WHO version of the ICD‐8) to identify all cases of type 1 diabetes. Beginning in 1995, visits to the emergency room and outpatient visits were included in the National Hospital Register (681 cases of type 1 diabetes). |
| Funding Source |
Government |
| Notes |
Conclusions: "These results do not support a causal relation between childhood vaccination and type 1 diabetes" |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| PCS/RCS ‐ exposed cohort selection |
Low risk |
Adequate ‐ National Board of Health |
| PCS/RCS ‐ non‐exposed cohort selection |
Low risk |
Adequate ‐ drawn from the same population |
| PCS/RCS ‐ comparability |
Low risk |
Adequate ‐ homogeneous age ‐ probable residual confounding |
| PCS/RCS ‐ assessment of outcome |
Low risk |
Adequate ‐ National Hospital Register |
| Summary Risk of Bias assessment |
Low risk |
Plausible bias is unlikely to have seriously altered the results. |
