The risk of idiopathic thrombocytopenic purpura after first and second measles, mumps, rubella (MMR) vaccine doses in children born in England 2000-2019.

We assessed the risk of Idiopathic thrombocytopenic purpura (ITP) after Measles Mumps Rubella vaccine (MMR) doses 1 and 2 in children in England born from 2000 to 2019. After linking hospitalised ITP episodes to MMR vaccine records, we used the self-control case-series method to assess the relative incidence in the 6-week period post vaccination. We also assessed the risk of ITP after dose 2 in those who had ITP after dose 1. We found an increased risk of ITP after dose 1 (relative incidence 2.38 (95% CI: 2.12-2.67)) with an attributable risk of 1 in 42,900 doses. We found no evidence of an increased risk after dose 2 (relative incidence 0.96 (95% CI: 0.81-1.13)). Furthermore, we found that the 336 children with ITP after dose 1 who had MMR dose 2 had no increased risk in the 6-weeks after this dose and that it is therefore safe to vaccinate these children.