Vice President Kamala Harris’ traveling delegation was delayed from departing Singapore for Vietnam on Tuesday due to “a report of a recent possible anomalous health incident in Hanoi,” her spokesperson said. That health incident, according to NBC News, was two possible cases of so-called Havana Syndrome, the mystery illness that has left embassy staff in Cuba, China, Austria, and China with hearing loss, memory loss, brain damage and nausea. Little is known about the illness but studies have speculated that it’s caused by microwave weapons, and some intel sources believe that Russia is responsible.

Just hours before Harris was set to leave for Vietnam, officials were told that unusual incidents had occurred over the weekend involving strange sounds, NBC reports. At least two U.S. personnel in Hanoi will be medevaced out of the country, the network says. Harris’ spokesperson said a decision was made to press ahead with travel to Vietnam “after careful consideration.” Harris is on a trip throughout Asia to meet with regional leaders.