When the woman left London on March 1, she had a sore throat and cough as she boarded a flight home to Vietnam, but no one noticed.
As she left the flight to Hanoi 10 hours later, another 15 people who were on the plane with her were infected, researchers said on Friday.
This story is one of two published on Friday, demonstrating how the coronavirus can spread on airline flights, and suggests that simply moving people away will not protect them completely.
In another incident, passengers on a flight from Boston to Hong Kong appeared to have infected two flight attendants.
Both cases involve long flights at the start of the pandemic before airlines began requiring face masks.
A team from Vietnam tracked a group of cases related to the flight, which arrived in Hanoi from London on March 2.
“A 27-year-old businesswoman from Vietnam, whom we identified as the probable case of the index, has been in London since early February,”
The woman boarded a flight to Hanoi on March 1.
“She was sitting in business class and continued to experience sore throats and coughs throughout the flight,” the researchers added.
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 her and found 12 fellow business class passengers, two economy class passengers and one crew member also infected.
Investigators said there was no other likely way for any of the 15 others to be infected other than exposing the sick patient to the flight.
“The most likely route of in-flight transmission is aerosol or drip transmission from case 1, especially for business class occupants,” they wrote.
“We conclude that the risk of SARS-CoV-2 transmission on board during long flights is real and has the potential to cause COVID-19 clusters of significant size, even in business class – similar settings with spacious seating far beyond the established distance used to determine close contact in aircraft, “wrote Hahn’s team.
“While COVID-19 poses a global pandemic threat in the absence of a good care test, better infection prevention measures are needed on board and arrival control procedures to make flying safe.”
In the second incident, the couple flew from Boston to Hong Kong in business class on March 9. Both showed symptoms when they arrived and were diagnosed with coronavirus.
“Genetic sequencing connects all four cases. The almost full-length viral genomes of all four patients are 100% identical,” wrote Watson-Jones and colleagues.