COVID-19 transmission on flights 'extremely rare,' Dr. Tam says

Canada's chief public health officer said today there's little evidence — if any — of COVID-19 transmission among passengers travelling by air.

Speaking to reporters at a COVID-19 briefing, Dr. Theresa Tam said that while the Public Health Agency of Canada (PHAC) is aware of reports that some COVID-19-infected people have travelled to Canada by air, there have been few documented cases of the virus actually being passed to others travelling on those same flights.

"There have been very few reports, extremely rare reports, actually, of transmission aboard aircraft," Tam said. "Very, very little."

In fact, Tam said she's not aware of any in-flight transmission being reported to provincial public health authorities. "We have not received that kind of report," she said, adding officials should relay that sort of information to her agency if they have it.

Tam said the negligible number of cases reported from flying is likely attributable to the strict cleaning measures that airlines have implemented since the onset of the pandemic.

For example, Air Canada — the country's largest carrier — passes cabin air through High Efficiency Particular Air (HEPA) filters about 20 to 30 times per hour during flights. The result is a mix of filtered air and fresh air from the outside.

The filters are similar to those used in hospital operating rooms and, according to Air Canada, are extremely effective at trapping microscopic particles as small as viruses and bacteria, along with dust, pollen and moisture.

WestJet also uses a HEPA filter system and says it "captures and filters 99.99 per cent of all airborne particles so you can breathe a little easier."

The Calgary-based airline also has implemented a cleaning process called "fogging," which sees the entire aircraft interior regularly disinfected with a hydrogen peroxide-based cleaner.

"I think we are learning more and more about some of the technologies, if you like, in terms of the ventilation and the way that the aircraft ventilation works. The modern aircraft is actually really good in terms of air exchanges and the way airflow occurs in the cabin," Tam said.

Tam said these ventilation systems — together with mandatory mask policies and instructions to passengers to keep to their seats and face forward while in flight — have made planes comparatively safe places to be during this pandemic.

Tam pointed out, however, that the in-flight experience is just one aspect of air travel. She said passengers can still be exposed to COVID-19 while travelling to and from the airport or waiting in an airport lounge.

She said that, for now, Canada will maintain its mandatory 14-day quarantine period for returning foreign travellers to reduce the potential for community spread. The airline industry has been ravaged by government-imposed travel restrictions and quarantines; Air Canada alone has reported hundreds of millions of dollars in losses.

Tam said the government is monitoring a PHAC-sponsored pilot project in Alberta that allows returning travellers to take a series of tests rather than isolate for two weeks. Ontario Premier Doug Ford has said he'd like to see a similar program in place in the country's largest province.

Safer than shopping?

Tam's comments follow reports out of the U.S. that also found the rate of in-flight COVID-19 transmission is minimal.

A Harvard University study released late last month found that flying may actually be safer than other routine activities, like going to the grocery store.

Researchers at the university's T.H. Chan School of Public Health found that even though air is recirculated back into the cabin during a flight, the high-quality filters used on most commercial airliners mean virus droplets from one passenger are unlikely to infect another.

The "layered approach, with ventilation gate-to-gate, reduces the risk of SARS-CoV-2 transmission onboard aircraft below that of other routine activities during the pandemic, such as grocery shopping or eating out," the study said.

The ventilation system isn't enough on its own, however. Harvard's researchers said masks, frequent cabin cleaning and a robust screening system for symptomatic passengers also play critical roles in keeping travellers healthy.

In fact, the study concluded that the use of face masks is "the most essential part of a comprehensive set of measures to reduce COVID-19 during air travel."

The study was sponsored by a major U.S. airline lobbying group, Airlines for America, but Harvard researchers said their findings and recommendations are "independent conclusions."

Another study conducted by the U.S. Department of Defence also found ventilation systems and stringent masking policies have made onboard transmission rare.

Through a simulation study of airflow onboard a United Airlines Boeing 777 aircraft, the military researchers found that about 99.99 per cent of particles were filtered out of the cabin within six minutes due to fast air circulation, downward air ventilation and aircraft filtration systems.

It estimated that, in order to receive an infectious dose, a passenger would need to fly 54 hours on a plane with an infected person.

The research was conducted over six months and involved 300 tests during 38 hours of flight time and 45 hours of ground testing.

The tests were done by releasing particles the same size as the novel coronavirus across the entire cabin by section. Each section had 42 sensors representing passengers.