Dendrogram illustrating the genetic relationship of H. influenzae strains isolated from cases of invasive infections of vaccinated patients (as determined by PFGE) to prevaccination Hib isolates. Strains from vaccinated children: 37398 (b), 2999 (b), 67299 (b), 52901 (b), 42402 (b), 70097 (nontypeable), 90797 (nontypeable), and 38398 (nontypeable). Prevaccination H. influenza type b isolates: 23095, 1494, 2995, 4194, 11194, 4394, 0994, and 3295. The x axis represents percentages of the genetic relationship.