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Three studies published late last week describe the transmission of COVID-19 in flight, one of which involves a single symptomatic passenger who likely infected at least 12 others during an international flight.
Seat proximity and increased risk
The first study, published in Emerging infectious diseases, involved an epidemiological investigation of all traceable passengers and crew members on a 10-hour Vietnam Airlines Flight 54 (VN54) from London to Hanoi, Vietnam, on March 1 that resulted in 15 sick people in addition to the index patient.
Researchers interviewed, tested and quarantined passengers and crew and tracked their close contacts to estimate the likelihood of transmission of SARS-CoV-2, the virus that causes COVID-19, on the flight and to identify factors of risk of propagation in flight.
Of the 16 crew members and 168 passengers tested, 15 (8.2%) tested positive for the new coronavirus, 12 (75%) of whom had been seated in business class with the symptomatic passenger, for an attack rate of 62% in that stretch. of the 274-seat plane. The other infected travelers had been sitting economy class and may have had contact with the index patient upon arrival at immigration or baggage claim.
Of the 12 infected passengers in business class, 8 (67%) developed symptoms after an average of 8.8 days after arrival in Hanoi. None had symptoms during the flight.
Sitting close to the sick passenger was strongly linked to an increased risk of infection. Eleven of the 12 infected passengers seated one or two seats away (92%) tested positive for COVID-19, compared with just 1 (13%) more than two seats away (risk index, 7.3) .
Of the 1,300 close contacts of crew members and passengers, 5 people (0.4%) tested positive for coronavirus, 3 of whom were members of the home staff of the index patient, who was the only symptomatic passenger and reported contact. before the flight with his sister. a confirmed COVID-19 patient.
The authors wrote: “The most likely route of transmission during flight is transmission by aerosols or droplets from Case 1, especially for people seated in business class.” They added: “We did not find strong evidence to support alternative transmission scenarios.”
The authors noted that thermal temperature detection and self-reporting of symptoms at the airport did not prevent the infected person from boarding. As is clear from this research, long flights can lead to ideal conditions for “superpreaders” events, they added.
Industry guidelines are insufficient, say the authors
Current international air travel industry guidelines characterize the probability of in-flight transmission of SARS-CoV-2 as very low and recommend only the use of face masks, not physical distancing in the face of blocking the middle seats, the officials said. researchers.
“Our findings challenge these recommendations,” they wrote. “The transmission on flight VN54 was clustered in business class, where the seats are already more widely spaced than in economy class, and the infection spread well beyond the existing 2 rows or 2 meters [6.6 feet] The recommended rule for the prevention of COVID-19 on airplanes and other public transport would have caught. ”
The findings reveal the need for stricter infection detection and control measures before and during flights, the researchers said, adding that systematic testing and quarantine policies for inbound passengers may also be justified in countries with low levels of community spread and high risk of cases. import and low contact tracing capabilities. Vietnam now requires proof on arrival and a 14-day quarantine.
“We conclude that the risk of on-board transmission of SARS-CoV-2 during long flights is real and has the potential to cause sizable COVID-19 clusters, even in business-class-like environments with roomy seats well beyond set distance used to define close contact in aircraft, “the authors said.
“As COVID-19 poses a global pandemic threat in the absence of good testing at the point of care, better infection prevention measures on board and arrival screening procedures are needed to make flying safe.”
Characteristic virus genome sequence
Another study in the same journal details the probable in-flight transmission of COVID-19 in two passengers and two crew members on a 15-hour flight from Boston to Hong Kong on March 9.
Infected travelers were diagnosed with coronavirus at local healthcare providers 5 to 11 days after arrival. They included a business class married couple and two flight attendants, one of whom had served the couple during the flight.
Genomic sequencing showed that the viruses from the four infected travelers were identical, unique, and part of a clade (group of viruses that evolve from a single ancestor) not previously seen in Hong Kong, which the authors strongly suggest that the virus was transmitted during the flight. Similar virus sequences were subsequently identified in Toronto, New York City and Massachusetts, all of which the couple had visited.
The authors said the evidence suggests the married couple became infected in North America and passed the virus on to flight attendants.
“The SARS-CoV-2 test results have been positive for hundreds of flight attendants and pilots; at least 2 have died,” they wrote. “Our results show that SARS-CoV-2 can be transmitted on airplanes. To prevent transmission of the virus during travel, infection control measures must continue.”
Traveling with symptoms
A third study, an epidemiological analysis published in Travel medicine and infectious diseases, demonstrated probable transmission of COVID-19 in flight in five passengers. Researchers in Athens, Greece, conducted contact tracing of 2,224 passengers and 110 crew members on 18 international flights arriving or departing from Greece from February 26 to March 9.
They identified 21 COVID-19 index cases and 891 close contacts, defined as passengers sitting within 2 meters of an infected passenger for at least 15 minutes or crew members who were close to them. Of the close contacts, four passengers and one crew member tested positive for COVID-19. Six index patients had symptoms during their flight.
The infected close contacts, which included three members of the same family, had traveled on the same 2-hour flight as two infected travelers who had been part of a pilgrimage to Jerusalem.
“The exposure of the two pilgrim index cases in Jerusalem and the subsequent spread of the disease during the flight can be justified considering that pilgrims constitute a group of travelers at high risk of contracting respiratory diseases due to their exposure to overcrowded conditions and by mixing with other people from different countries where local transmission of SARS-CoV-2 could have been documented, “the authors said.
