O’Brien’s Vietnamese hosts regarded their guest and his entourage as human petri dishes and restricted the delegation to a single floor of the luxurious Metropole hotel in Hanoi. Room service meals were left outside the U.S. guests’ doors, and Vietnamese officials in head-to-toe protective gear administered virus tests.

The Air Force flight crew on O’Brien’s plane wasn’t allowed to stay in the country; the aircraft was sent to Thailand while the national security adviser conducted his business in Vietnam.

The caution proved astute. Later, on the Philippines leg of the trip, one crew member developed a fever and tested positive for coronavirus. The crewman and two National Security Council aides who had been near them isolated themselves at a hotel in Manila, and O’Brien’s plane left for the U.S. without them. NSC aides were alerted Wednesday morning that two more crew members have COVID-19.

Officials in the Philippines weren’t as strict, but required O’Brien’s team, immediately after they deplaned, to follow the government mandate on wearing plastic face shields over masks in indoor public spaces.