A case-control study to assess the risk of immune thrombocytopenia associated with vaccines.

The cause of immune thrombocytopenia (ITP) remains unknown. Studies have suggested immunizations as possible triggering factors of ITP through molecular mimicry. This case-control study explored potential associations between adult ITP and various routinely administered vaccines. A network of internal medicine and hematology centers across France recruited 198 incident (ie, newly diagnosed) cases of ITP between April 2008 and June 2011. These cases were compared with 878 age- and sex-matched controls without ITP recruited in general practice. Information on vaccination was obtained from patients' standardized telephone interviews. Sixty-six of 198 cases (33.3%) and 303 of 878 controls (34.5%) received at least 1 vaccine within the 12 months before the index date. We found no evidence of an increase in ITP after vaccination in the previous 6 or 12 months (adjusted odds ratio [OR] for the previous 12 months = 1.0; 95% confidence interval, 0.7-1.4). When the 2-month time window was used, higher ORs were observed for all vaccines (OR = 1.3). This increase was mainly attributable to the vaccination against diphtheria-tetanus-pertussis-poliomyelitis (OR = 1.5) and was not statistically significant. The results of the present study show that in an adult population, the exposure to common vaccines is on average not associated with an observable risk of developing ITP.