db‐France 2008.
| Study characteristics | ||
| Methods | Self‐controlled cases series. Study based on Vaccine Safety Datalink investigating association of immune thrombocytopenic purpura and MMR | |
| Participants | Children aged 12 to 23 months with ITP identified from VSD database for the years 1991 to 2000, who had been vaccinated with MMR whilst actively enrolled in their respective MCOs. For each child, follow‐up time was limited to the 365 days before and after MMR vaccination. Vaccinated children with ITP that occurred outside this follow‐up window were excluded. The criteria for cases were defined as children aged < 18 years with a platelet count of 50,000/L with normal red and white blood cell indices, the presence of clinical signs and symptoms of spontaneous bleeding, and the absence of fever. A case was excluded if in the 6 weeks before diagnosis the child had been exposed to platelet‐depleting medication (phenytoin, valproic acid, or sulfonamide antibiotics) or infected with wild‐type varicella or Epstein‐Barr virus. |
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| Interventions | Exposure to MMR vaccine (composition not provided in the study report) Exposed period: 42 days after MMR vaccination Unexposed period: defined as the time periods before and after the exposed period. Period of 6 weeks immediately preceding MMR vaccination was excluded from analysis because this represents a period when a child is most likely to be healthy (the healthy‐vaccinee) and may underestimate the background incidence of ITP. |
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| Outcomes | ITP diagnoses within 42 days from immunisation | |
| Funding Source | Government | |
| Notes | ||
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| SCCS/PTC ‐ case selection | Low risk | Adequate ‐ independent validation |
| SCCS/PTC ‐ exposure | Low risk | Adequate ‐ secure record ‐ but probable selection bias |
| SCCS/PTC ‐ observation and exposure risk period | Low risk | Adequate ‐ observation periods are well‐defined, exposure period appears to be well‐documented |
| SCCS/PTC ‐ comparability | Low risk | Adequate adjusted for age, sex, MMR doses |
| Summary Risk of Bias assessment | Low risk | Plausible bias is unlikely to have seriously altered the results. |