The Trump administration on Monday barred US citizens in the Democratic Republic of the Congo from returning home amid an Ebola outbreak that continues to outpace response efforts.

Reuters first reported late Monday that Americans currently in the DRC or those who have recently traveled to the Ebola-stricken country have been put on a “do-not-board” list. They cannot travel back to the US until they have spent 21 days in a third country. The order, taken under a transportation authority known as Title 49, was independently confirmed by Politico on Tuesday.

Both outlets noted that roughly two dozen Americans who had been set to board flights home on Tuesday have already been blocked by the new rule. It remains unclear if the bar also applies to government workers. The Centers for Disease Control and Prevention has at least two dozen employees working in the DRC.

The move adds to the already extremely stringent and controversial travel restrictions imposed by the Trump administration in an effort to wall itself off from the outbreak. Health experts continue to be critical of such restrictions, as they have historically been unsuccessful and harmful. Specifically, they discourage countries and people from being transparent about outbreaks and disease risks, hurt economies, and create stigma. There is also concern that such restrictions will limit humanitarian aid workers.

Ebola threat

Ebola is not a disease that readily spreads like respiratory viruses. It transmits via contact with bodily fluids while people are actively sick or recently deceased. It has been described as a disease of compassion because it primarily spreads to family, loved ones, caregivers, and medical personnel who have extensive contact with cases when they are most ill and infectious. In other words, it’s not a disease one would pick up by sitting next to someone who is merely coughing on an airplane.