A new study has detailed how a single traveller infected four others on a flight from Dubai to New Zealand, despite testing negative before they boarded the flight.
The government-funded New Zealand study into the flight raises questions about the safety of international travel during the pandemic, even when the precaution of pre-flight testing is taken.
The infections occurred on a flight from Dubai to New Zealand in September.
In total, seven cases from the flight were identified in managed isolation and scientists believe that four of those cases picked up the virus during the 18-hour flight.
There were 86 passengers onboard the flight.
Those seven passengers came from five different countries before travelling on the flight from Dubai, but genomic testing suggested that four infections took place onboard as they carried genome sequences from Switzerland, the country of origin of the source case.
That source case had tested negative on a polymerase chain reaction (PCR) test 48 hours before their flight.
David Freedman, an infectious-disease specialist at the University of Alabama, told The Washington Post that the case highlight the difficulty in ensuring flights remain virus-free.
"This case speaks to how hard it is to keep infected people off a flight, even if you do PCR testing in a narrow window of time before the flight," Freedman said.
"The original case most likely became infectious after he took the pre-flight test, but in fact was not symptomatic until 71 hours after the flight."
The report also states that "transmission events occurred despite reported use of masks and gloves in-flight".
The findings contradict a US Department of Defence study that found that a contagious person would need to sit next to a fellow passenger for at least 54 hours, declaring that the risk of transmitting the virus on planes was "low".
"These seven cases were found to have been seated within four rows of each other during the approximately 18-hour flight," the NZ study states.
"Recent studies have presented conflicting findings of the risks associated with in-flight transmission. We therefore undertook a comprehensive investigation to determine the potential source of infection."
Justin Tighe-Umbers, executive director of the Board of Airline Representatives of New Zealand, told the Herald that the risk of catching the virus during flights remains extremely low – if people follow safety measures and use masks.
Tighe-Umbers noted that of the more than 62,000 passengers who had entered quarantine up to October 20, only 215 had tested positive for Covid-19.
"To put it all into perspective, that's 0.34 per cent of the total number of people who arrived on many international flights."
He argued that "the blanket 14 days MIQ systems we have in place now could be intelligently remodelled" if risk assessments were done on a traveller's country of origin.
The results of the study could spell trouble for US travellers as they crowd airports to get away for the country's annual Thanksgiving holiday.
Dr Anthony Fauci told CBS' Face the Nation on Sunday that the "people at airports", despite federal guidance to avoid travel, "are going to get us into even more trouble than we're in right now".
He noted that new Covid-19 cases from Thanksgiving won't become evident till weeks later, making it "very difficult" as the virus spirals out of control heading into colder weather and the December holiday season.
- Additional reporting, AP