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.

Staff at the Centers for Disease Control and Prevention have been ordered to immediately stop engaging with the World Health Organization, a move that affects critical work on influenza surveillance and disease outbreaks across the globe,