Workers at the U.S. Centers for Disease Control and Prevention have been ordered to stop working with the World Health Organization immediately. The hasty directive came as a surprise to CDC employees, many of whom are working on crucial public health projects aimed at preventing major outbreaks of Marburg virus, mpox and bird flu. Trump’s day one executive order withdrawing the U.S. from the WHO requires a one-year notice, the approval of Congress, and for the U.S. to still fulfill its financial commitment for the fiscal year.