Theoretical Biology and Biophysics Group, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States of America.|Human Vaccine Institute, Duke University Medical Center, Durham, North Carolina, United States of America.|Human Vaccine Institute, Duke University Medical Center, Durham, North Carolina, United States of America.|Theoretical Biology and Biophysics Group, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States of America.