From the Medical Scientist Training Program (K.E.L.), University of California, San Francisco; Biomedical Sciences Graduate Program (K.E.L., I.A.H.), University of California, San Francisco; Weill Institute for Neurosciences (R.D.S., I.A.H., P.S.R., A.R., M.R.W.), University of California, San Francisco; Department of Neurology (R.D.S., I.A.H., P.S.R., A.R., M.R.W.), University of California, San Francisco; Institut de Recerca Pediàtrica Hospital Sant Joan de Déu (D.C.-A., C.L., A.V.-R., C.M.-A.), Barcelona, Spain; Chan Zuckerberg Biohub (J.E.P., W.W., C.K.C., E.D.C., J.L.D.), San Francisco; Department of Biochemistry and Biophysics (L.M.K., H.A.S., K.C.Z., J.L.D.), University of California, San Francisco; CIBER Epidemiología y Salud Pública (CIBERESP) (C.L., M.C., C.M.-A.), Health Institute Carlos III; Department of Pediatrics (C.L.), Universitat de Barcelona, Barcelona; Enterovirus Unit (M.C.), Spanish National Centre for Microbiology, Instituto de Salud Carlos III, Madrid, Spain; Division of Infectious Diseases (C.L.), Department of Medicine, University of California, San Francisco; and Department of Medicine. Universitat Internacional de Catalunya (C.M.-A.), Barcelona, Spain.