When the woman left London on March 1, she had a sore throat and cough as she boarded a flight to Vietnam, but no one noticed.
By the time she landed in Hanoi 10 hours later, 15 other people aboard the plane had been infected, the researchers reported on Friday.
The story is one of two published Fridays showing how coronoviruses can spread on airline flights, and suggests that simply excluding people a bit will not fully protect them.
In another incident, passengers on a flight from Boston to Hong Kong infected two flight attendants.
Both cases involved long flights at the onset of the epidemic, before airlines required a face mask.
A team from Vietnam tracked a group of cases involving a flight arriving from London to Hanoi on 2 March.
Nguyen Kang Khan of Hanoi’s National Institute of Hygiene and Epidemiology wrote, “A 27-year-old businessman from Vietnam, whom we identified as a potential index case, was based in London in early February.”
The woman was flying to Hanoi on 1 March.
“She sat in business class and continued to experience a sore throat and cough throughout the flight,” the researchers said.
She went to the hospital three days after landing and tested positive for the virus. Health officials tracked 217 passengers and crew who were on the flight with him and 12 fellow business class passengers, two economy class passengers and a crew member were also infected.
Investigators said that in addition to coming in contact with a sick patient on the flight, any of the other 15 people could be infected.
He wrote, “The most likely route of transmission during flight is aerosol or droplet transmission, especially for persons in business class.”
“We conclude that the risk for on-board transmission of SARS-CoV-2 during long flights is real and has the potential to cause COVID-19 clusters, even in business class – As Khap’s team, with settings beyond the huge seating arrangement, wrote, “the distance used to define close contact on an airplane.”
“As long as COVID-19 presents the risk of a global pandemic in the absence of a good point-of-care test, better on-board infection prevention measures and arrival screening procedures are needed to make the flight safer.”
In the second incident, a couple flew from Boston to Hong Kong in business class on 9 March. Symptoms were demonstrated after both arrived and a diagnosis of coronovirus was made.
Watson-Jones and colleagues wrote, “Genetic sequencing linked all four cases. The full-length viral genomes of all four patients were 100% identical.”