Cases of GBS identified among cohort members 19-<22 years old will be identified from administrative claims data, and adjudicated through review of abstracted medical record information in a manner equivalent to that for cohort members 11-<19 years old. These cases will be quantified, and their clinical presentation described and compared with that of cases among 11-<19 year olds, with regard to at least the following factors: proportion of cases classified as definite GBS cases, severity of illness as measured by mortality, hospitalization for GBS, total duration of hospitalizations in days, mechanical ventilation required, total number of days of mechanical ventilation, intravenous immunoglobulin therapy, plasmapheresis, and immunosuppressive therapy. Similar comparisons will be made regarding the clinical presentation of GBS among MCV4 vaccinees compared to non-vaccinees.