1. Center for Inference and Dynamics of Infectious Diseases, Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center; Seattle WA U.S.A.
2. Department of Biostatistics; School of Public Health, University of Washington; Seattle WA U.S.A.
3. Department of Biostatistics, Gillings School of Global Public Health; University of North Carolina at Chapel Hill; Chapel Hill NC U.S.A.