How risky is flying during Covid-19 pandemic? Studies show methods used by airlines to prevent spread may not work
Air travel has seldom looked the way it does right now amid the Covid-19 pandemic. But how risky is air travel during a pandemic? Two new studies reveal that coronavirus can also spread on airline flights, and suggest that simply spacing people out may not protect them completely.
In the first study, to assess the role of in-flight transmission of Covid-19, researchers from Vietnam investigated a cluster of cases among passengers on a 10-hour-long commercial flight that arrived in Hanoi from London on March 2. A 27-year-old businesswoman from Vietnam was identified as the probable index case (case 1). The authors traced 217 passengers and crew to their final destinations and interviewed, tested, and quarantined them. Among the 16 persons in whom Covid-19 infection was detected, 12 (75%) were passengers seated in business class along with the only symptomatic person, demonstrating an attack rate of 62%. Seating proximity was strongly associated with increased infection risk, with a risk ratio of 7.3. The authors say that they found no strong evidence supporting alternative transmission scenarios. In-flight transmission that probably originated from one symptomatic passenger caused a large cluster of cases during a long flight, they explain.
“In-depth epidemiologic investigations strongly suggest that 1 symptomatic passenger transmitted SARS-CoV-2 (the virus that causes Covid-19) infection during the flight to at least 12 other passengers in business class. All 12 additional cases in the business class met the definition of probable secondary cases,” they write in the US Centers for Disease Control and Prevention’s Emerging Infectious Diseases journal.
The team suggests that guidelines for preventing coronavirus infection among air passengers should consider individual passengers’ risk for infection, the number of passengers traveling, and flight duration. “We conclude that 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. As long as Covid-19 presents a global pandemic threat in the absence of a good point-of-care test, better on-board infection prevention measures and arrival screening procedures are needed to make flying safe,” the investigators suggest.
Describing the case, the report says that the businesswoman had been based in London since early February. She and her sister had traveled to Milan and then to Paris for the yearly Fashion Week before returning to London on February 25. They continued to stay in London until February 29, when the businesswoman started to experience a sore throat and cough while attending meetings and visiting entertainment hubs with friends. On March 1, she boarded flight Vietnam Airlines flight 54 (VN54). She was seated in business class and continued to experience the sore throat and cough throughout the flight. By the time she left the flight, 15 others who were on the flight with her had been infected, including 14 among passengers and 1 crew member. Of the 15 persons with flight-associated cases, 12 (80%) had traveled in business class with case 1, and 2 travelers and 1 flight attendant had been in economy class. Her signs and symptoms (fever, sore throat, fatigue, and shortness of breath) progressed further after arrival, and she self-isolated at her private residence in Hanoi and had contact with household personnel only. On March 5, the businesswoman sought care at a local hospital in Hanoi where she tested positive for coronavirus.
“Among persons in business class, the attack rate was 62% (13 out of 21). Among passengers seated within 2 meters from case 1 (the businesswoman), which we approximated in business class to be less than 2 seats away, 11 (92%) were SARS-CoV-2–positive compared with 1 (13%) located over 2 seats away. Of the 12 additional cases in business class, symptoms subsequently developed in 8 (67%); median symptom onset was 8.8 days. None of the additional cases showed Covid-19 symptoms while onboard VN54,” the findings state. It adds, “Our investigation did not reveal strong evidence supporting potential SARS-CoV-2 exposure either before or after the flight for any of the additional persons with flight-associated cases other than having traveled on the same flight as case 1.”
According to the analysis, the most likely route of transmission during the flight is aerosol or droplet transmission from case 1, particularly for persons seated in business class. Contact with case 1 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, they add. “Our findings have implications for international air travel, especially because several countries have resumed air travel despite ongoing SARS-CoV-2 transmission. Thermal imaging and self-declaration of symptoms have clear limitations, as demonstrated by case 1, who boarded the flight with symptoms and did not declare them before or after the flight. Second, long flights not only can lead to the importation of Covid-19 cases but also can provide conditions for superspreader events,” emphasizes the team.
The authors say that the latest guidance from the international air travel industry classifies the in-flight transmission risk as very low and recommends only the use of face masks without additional measures to increase physical distance on board, such as blocking the middle seats The current findings challenge these recommendations, they state.
“Transmission on flight VN54 was clustered in business class, where seats are already more widely spaced than in economy class, and the infection spread much further than the existing 2-row or 2 meters rule recommended for Covid-19 prevention on airplanes and other public transport would have captured. Our findings call for tightened screening and infection prevention measures by public health authorities, regulators, and the airline industry, especially in countries where substantial transmission is ongoing,” they conclude.
Second study
A research team identified a cluster of four persons with Covid-19 associated with a commercial flight that departed from Boston on March 9 and arrived in Hong Kong on March 10, 2020. “The airplane, a Boeing 777-300ER, flew for about 15 hours and carried a maximum of 294 passengers. The cluster comprised 2 passengers and 2 cabin crew members,” they say.
A married couple – a 58-year-old man and a 61-year-old woman – flew from Boston to Hong Kong in business class on March 9. They arrived in Hong Kong on March 10. No public record indicates whether these 2 passengers were symptomatic during the flight. They both showed symptoms after they arrived and were diagnosed with coronavirus. Contact tracing revealed two flight attendants who tested positive for the virus. One was an asymptomatic 25-year-old man, identified through contact tracing by the Hong Kong government and the airline as a close contact of the couple. He served the couple during the flight. The fourth person was a 51-year-old female Hong Kong-based flight attendant on the same flight. She developed a fever and cough on March 18 and was subsequently hospitalized. There is no publicly available information of her travel history before the flight or her contacts with the other patients on or after the flight, reveals analysis. According to the investigators, the results demonstrate that Covid-19 can be transmitted on airplanes.
The near full-length viral genomes from all four patients were 100% identical. “Their virus genetic sequences are identical, unique, and belong to a clade not previously identified in Hong Kong, which strongly suggests that the virus can be transmitted during air travel,” the authors write in the Emerging Infectious Diseases journal. They conclude: “Given the case histories and sequencing results, the most likely sequence of events is that one or both of passengers A and B (the couple) contracted SARS-CoV-2 in North America and transmitted the virus to flight attendants C and D (flight attendants) during the flight. The only location where all 4 persons were in close proximity for an extended period was inside the airplane. Our results strongly suggest the in-flight transmission of SARS-CoV-2. No other Covid-19 cases associated with this flight have been identified. To prevent transmission of the virus during travel, infection control measures must continue.”