The New Zealand researchers looked at an outbreak among passengers who had traveled on the same 18-hour Emirates flight from Dubai, United Arab Emirates, to Auckland, New Zealand in late September. Seven of the 86 passengers onboard later tested positive while in managed 14-day quarantine.
Mask use was not mandatory on the flight. Five of the infected passengers self-reported mask and glove use on the plane while two did not.
Of the seven infected passengers, five had tested negative within 48 hours before the flight. The outbreak was linked through DNA analysis to one passenger who had tested negative for Covid-19 with a polymerase chain reaction (PCR) test within 48 hours of the flight. That infected passenger was contagious but pre-symptomatic onboard the plane, and subsequently infected at least four other passengers.
“All seven of the SARS-CoV-2 genomes were genetically identical, with the exception of a single mutation in one case,” found the researchers. “Four of these six related genome sequences were from Switzerland, the country of origin of the suspected index case.”
“By combining information on disease progression, travel dynamics and genomic analysis, we conclude that at least four in-flight transmission events of SARS-CoV-2 likely took place,” the scientists wrote. “These transmission events occurred despite reported use of masks and gloves in-flight.”
In most countries, public health officials have no way of monitoring passengers after their flight. But New Zealand authorities manage the quarantines for arriving passengers, which meant that all the passengers in the study were monitored and retested during their 14-day isolation.
That some of the infected passengers had tested negative before the flight and then positive several days afterward during quarantine “indicates some of the complexities in determining the value of pre-departure testing,” noted the team. “These findings underscore the importance of considering all international arrivals into New Zealand as potentially infected with SARS-CoV-2 even if pre-departure tests have been undertaken, social distancing and spacing have been followed and personal protective equipment has been used in flight.”
Two months ago, a pair of studies — one from Vietnam and the other from a multi-national group of institutions — both found that Covid-19 is transmissable on long-haul airline flights.
“Most viruses and other germs do not spread easily on flights because of how air circulates and is filtered on airplanes,” according to CDC travel guidance. “However, social distancing is difficult on crowded flights, and sitting within 6 feet of others, sometimes for hours, may increase your risk of getting COVID-19.”