Incidence and Relative Risk of Clinically Serious Outcomes Following MMR Receipt in Adolescents and Adults (Age ≥ 9 Years), Vaccine Safety Datalink, 2010–2018. Abbreviations: 95 % CI = 95 % confidence interval; MMR = measles, mumps, and rubella vaccine; GBS = Guillain-Barré syndrome; ITP = immune thrombocytopenia. aEvents confirmed via medical record review. bThe number of doses is different for seizures because there were 10 potential cases of seizure identified in automated data that were unable to be confirmed or refuted via medical record review, 6 in the risk window and 4 in the control window. For analysis, these doses were excluded.