A single passenger spread Covid-19 to 15 other people aboard a flight from London to Hanoi, Vietnam, according to a study published Friday by the Emerging Infectious Diseases journal, which is published by the Centers for Disease Control and Prevention.
Researchers from Vietnam's National institute of Hygiene and Epidemiology identified a 27-year-old woman from Vietnam who had a sore throat and a cough before the flight as the source of the outbreak. Twelve passengers in business class and two in economy, as well as a crew member, were infected on the March 1 flight, the study says.
Upon arrival, her symptoms progressed further, and she tested positive four days later.
By March 10, contact tracing was conducted for all 217 people aboard the Vietnam Airlines flight, the study said. While people aboard the flight had traveled to 15 provinces in Vietnam, there was no "strong evidence" supporting potential Covid-19 exposure to others outside those on the flight.
"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," the study's authors wrote. "Our findings call for tightened screening and infection prevention measures by public health authorities, regulators, and the airline industry."
Health officials said that at the time of Flight VN54's arrival, passengers and crew members were not required to wear masks in airplanes or at airports. All passengers from Covid-19-infected areas, including the U.K., were screened by thermal imaging upon arrival, but the study does not say whether the woman was flagged for symptoms.
Since March, the CDC has found that nearly 11,000 people were exposed to the coronavirus on flights, The Washington Post reported.
In its public health guidance, the CDC says that viruses are not easily spread on planes because of their air filtration systems but that sitting within 6 feet of other people and touching frequently used surfaces on long-haul flights can increase the risk of contracting Covid-19.
The authors of the Vietnam flight study recommended mandatory face coverings, routine hand-washing and testing protocols, and quarantine policies for arriving passengers from countries of high risk.
They added: "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."
CORRECTION (Sept. 25, 2020, 1:45 p.m. ET): A previous version of this article misstated who conducted a study that found that the plane passenger had infected 15 others. The study was conducted by researchers for Vietnam's National institute of Hygiene and Epidemiology and appeared in the Emerging Infectious Diseases journal, which is published by the CDC. It was not a CDC study, and none of the study's authors are affiliated with the CDC.