U.S. public health officials have been told to stop working with the World Health Organization, effective immediately. A U.S. Centers for Disease Control and Prevention official, John Nkengasong, sent a memo to senior leaders at the agency on Sunday night telling them that all agency staff who work with the WHO must immediately stop their collaborations and “await further guidance.” Experts said the sudden stoppage was a surprise and would set back work on investigating and trying to stop...