One person with COVID-19 infected 15 others during a long-haul flight from London to Vietnam in early March, according to a new analysis.
The study from the Centers for Disease Control and Prevention, which was released ahead of its final publication in November, is one of the first to analyze the dangers of in-flight transmission of the SARS-CoV-2 virus.
While the airline industry has judged the risk for in-flight transmission to be very low, the researchers noted that long flights in particular have become a matter of increasing concern as many countries have started lifting flight restrictions despite ongoing the ongoing pandemic.
The researchers identified a 27-year-old woman in business class as the primary source of the outbreak. The woman first developed a sore throat and cough on Feb. 29. She boarded the plane March 1, and continued to experience those symptoms throughout the 10-hour flight.
She developed a fever, fatigue and shortness of breath upon arrival, and was diagnosed with COVID-19 five days later.
The woman was the only symptomatic person on the flight, but researchers found she had infected 12 people in business class, two passengers in economy and one flight attendant in economy.
The most likely route of transmission during the flight is aerosol or droplet transmission, the researchers found, particularly for people seated in business class. Contact with the infected woman might also have occurred outside the airplane at the airport, in particular among business class passengers in the pre-departure lounge area or during boarding.
Contact with the two economy class cases might have occurred after arrival during immigration or at baggage claim.
The researchers said the role of fomites and on-board surfaces like tray tables or toilets remains unknown. Airline crew often use business class toilets while on board, which might explain the case among the crew serving in economy class, because no other potential source of infection could be established.
The flight took place March 1, before face masks were required or recommended on airplanes. Masks will certainly help reduce the risk of transmission, but the researchers said more on-board precautions and screening procedures should be taken, especially in the absence of a good test that can provide rapid results.
Transmission was clustered in business class, where seats are already more widely spaced than in economy class, and infection spread much further than the existing two-row or six-foot rule recommended for COVID-19 prevention on airplanes and other public transport would have captured.
"The risk for on-board transmission of SARS-CoV-2 during long flights is real and has the potential to cause COVID-19 clusters of substantial size, even in business class–like settings with spacious seating arrangements well beyond the established distance used to define close contact on airplanes," the study concluded.