1. Vaccine Study Center, Kaiser Permanente Northern California, Oakland, California (O.Z., J.B., B.F., N.L., K.G., N.P.K.)
2. Centers for Disease Control and Prevention, Atlanta, Georgia (K.D., J.D.)
3. Institute for Health Research, Kaiser Permanente Colorado, Denver, Colorado (J.G.)
4. Kaiser Permanente Center for Health Research, Portland, Oregon (A.N.)
5. Marshfield Clinic Research Institute, Marshfield, Wisconsin (J.G.D.).