According to a new study published by the American Centers for Disease Control and Prevention (CDC), on 2 March, one Covid-19 positive person infected a large number of other passengers during a 10-hours commercial flight between London and Hanoi.
The 27-year-old woman embarked the flight, unknowing to be positive, way before the obligation to wear a face mask came out.
The study shows how the traveler – who had symptoms such as sore throat – infected 12 business class passengers, two in economy and one crew member. In total, there were 217 people on the flight. The transmission during the flight occurs through aerosol or droplet; this highlights the importance to wear facial masks when on board and when close contact is unavoidable.
To assess the role of in-flight transmission of the coronavirus, the CDC investigated a cluster of cases among passengers on this long-haul flight. Affected individuals included passengers, crew, and their close contacts.
The CDC traced the 217 passengers and crew to their final destinations and interviewed, tested, and quarantined them. 16 people tested positive for Covid-19. 12 (75%) of them were business class passengers, thus seating close to the symptomatic person (attack rate 62%). Seating proximity is strongly associated with increased infection risk (risk ratio 7.3, 95% CI 1.2–46.2).
The CDC did not find any strong evidence to support other transmission scenarios. In-flight transmission that probably originated from 1 symptomatic passenger caused a large cluster of cases during a long flight. Guidelines for preventing the spread of infections among air passengers should take into consideration individual passengers’ risk for infection, the number of passengers, and the duration of the journey.