Staff at the US Centers for Disease Control and Prevention have been ordered to stop communicating with the World Health Organization, according to a new memo, dealing a significant blow to global health efforts.

Experts said the sudden stoppage was a surprise and would set back work on investigating and trying to stop outbreaks and brewing global threats.

Officials from the Centers for Disease Control and Prevention have been ordered to stop working with the World Heath Organization immediately, following President Donald Trump’s executive order withdrawing the U.

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 staff who work with the WHO must immediately stop their collaborations and “await further guidance.