There was no difference in the proportion of patients who received an immunization in the 6 months before illness onset or in the number of immunizations received, between clinical or autoantibody phenotypes, nor by age, gender, race, disease course or delay to diagnosis. Patients with a polycyclic illness course were more likely than patients with a monocyclic illness course to have received an immunization or to have received a measles-mumps-rubella (MMR) vaccine in the 6 months before illness onset (21 vs 6%; P = 0.023; OR 4.1; 95% CI 1.2, 13.9 and 50 vs 6%; P = 0.035; OR = 17.0; 95% CI 1.3, 223, respectively). Given the time period under study, it was not surprising that patients >7.5 years of age at diagnosis were more likely to have received a hepatitis B vaccine than younger patients (47 vs 12%; P = 0.002; OR 6.2; 95% CI 2.0, 19.7), whereas patients 47.5 years of age were more likely to have received a diphtheria-(pertussis)-tetanus vaccine (22 vs 6%; P = 0.033; OR 8.2; 95% CI 0.98, 69.8).