The issue focused on what the United States is doing on the ground to try to prevent the spread of the virus and what its potential consequences will be, said Dr. Thomas Frieden, the president of the CDC, in an interview on the program "World News Tonight with Diane Sawyer."

Dr. Robert F. Kennedy Jr., head of research and development at the NIH, said the virus is already known to spread in the body, and that there is no evidence that vaccines are needed to prevent the spread of