In the last few hours a study has been published, still in the preliminary phase, which describes a cluster that originated, according to the authors of the paper (Published on Emerging Infectious Diseases), on a 10-hour flight from London to Hanoi on 1 March.
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The description of the flight
An index case would have infected 15 people sitting in business class even more than two meters away (in the image above, the index case in red and the arrangement of the seats occupied by the infected people following the flight in orange). It is a young woman and her sister who had traveled to Milan and Paris for events related to fashion, then they had gone to London, from where they had taken the flight to Hanoi. It was March 1st, one of them had a little sore throat and cough, but no fever. At the time, airlines had not yet taken any measures to fight the virus, and the mask on board was not mandatory. There were 217 passengers and crew members on the flight. Twelve people flying in business class, two flying in economy class and one crew member tested positive in the days after the flight. We conclude that the risk of on-board transmission during long-haul flights is real and can create major outbreaks, even in areas such as business class, with more space between seats, Vietnamese researchers from the National Institute of Hygiene and Epidemiology in Hanoi write.
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Many doubts
However, the study has some peculiarities that do not make transmission during the flight so obvious: at least not for all reported cases. Apart from the lack of masks, half of the infected people were part of the contacts of the sick woman, which suggests that they could also have become infected after the flight, a possibility not excluded even by the authors of the research. In fact, the median onset of symptoms was 8.8 days after arrival: incubation also reaches 14 days, but the average of 5 days, so eight seems like a lot. The paper states that two infected people had symptoms 17 days later. Five of the 15 flight-associated cases experienced symptoms beyond the time 97.5% of people experienced symptoms. It is therefore unlikely that these five people have contracted it in flight. Regarding the remaining 10, we read that 3 people continued their journey on cruise ships where they could be infected.
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Conclusions
Airplanes are generally considered to be of limited risk for the transmission of Covid-19, due to the filtration and permanent renewal of the air. This would therefore be the first epidemiological study to show a large cluster originating in an airplane. In the present case, the flight was very long (10 hours) – which certainly increases the risk – and the use of a mask was not widespread. The most likely route of transmission is via aerosols or droplets during flight. Contact with the index case may also have occurred outside the aircraft, particularly among business class passengers on the flight in the lounge area before departure, the study reads. An exposure at risk (duration, symptomatic case, closed environment, distance but no mask), but we can’t be sure that the woman has really infected all 15 people. In any case, of course, it is not excluded that traveling by plane with sick people next to them can make people infected: proximity and a closed place (despite ventilation and masks) are risk factors, especially when prolonged proximity.
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September 19, 2020 (change September 19, 2020 | 9:08 pm)
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