There is scarce reliable data, so the understanding of how exactly COVID-19 transmits during flights is limited. Studies and experts, however, consistently highlight the need to wear face masks and maintain physical distance from other travellers.
One case study, published in the Centers for Disease Control and Prevention (CDC) Emerging Infectious Disease peer-reviewed journal in March, could suggest the importance of face masks and air filtration during flights. Researchers focused on the long-haul flight of EK488 from Dubai, United Arab Emirates, to Auckland, New Zealand. Using genomic sequencing, scientists found that four passengers on board became infected by one of two other passengers on the flight. Two of the passengers infected were not wearing face masks.
The study also noted an important caveat that relates to air circulation. Flight EK448 made a two-hour stopover in Kuala Lumpur, Malaysia, to refuel. While no passengers entered or exited the aircraft, the plane was inoperative for around 30 minutes, meaning the environmental control system — which regulates the cold air unit and air distribution — was not on.
Another study published by the CDC, using laboratory modelling, found that leaving the middle seat open can reduce COVID exposure by up to 57%. The research, however, did not take into account passengers wearing masks.
How does the plane’s air circulation work — and how effective is it against virus transmission?
When an aircraft’s ventilation system is in use, the risk of COVID transmission significantly decreases. This is how it works: Fresh, warmed and compressed air enters the cabin partly through the air-conditioning system.
In addition, passengers’ exhaled air is cleaned with HEPA (High-Efficiency Particulate Air) filters, which are also used in hospital operating rooms, for example. These filters are designed to retain 99.95% of airborne particles of a wide variety of sizes, greatly reducing the risk of infection.
The fresh air from outside and the filtered air from inside are then mixed and pushed back into the cabin. Depending on the size of the aircraft and the duration of the flight, the amount of fresh air supplied varies, as well as how often the air in the cabin is actually completely exchanged. According to Lufthansa, the air in a flight cabin of an Airbus320 consists of about 60% conditioned air from outside and about 40% filtered air from within the aircraft.
Reliable studies on ventilation systems in aircraft and the spread of COVID-19 during a flight are still lacking. But experts say that air circulation and filtration systems alone cannot completely protect against infection. HEPA filters can only clean particles that reach it — so passengers need to minimize risks, such as wearing face masks, to help avoid coming into contact with particles that did not reach the filter.
“On aircraft, what we found is a combination of ventilation systems that can remove up to 99% of COVID particles from the air, continuously cleaning the air in combination with face masks,” said Leonard Marcus, the director of Harvard’s Aviation Public Health Initiative, to DW.
The movement of passengers and cabin crew also plays a role, said Timo Ulrichs, an infection epidemiologist and professor at the Berlin-based Akkon University. When passengers and crew move about in the aircraft cabin, it can affect the direction of airflow, said Ulrichs, meaning certain air particles may linger in the cabin for longer than if passengers remain seated. This disruption, he added, could increase the risk of infection. The assessment is backed by Dieter Scholz, a professor of Aircraft Design, Flight Mechanics and Aircraft Systems at the Hamburg University of Applied Sciences. When referring to the risks associated with people moving inside the cabin, he told DW, “the viruses, the aerosols, can then also be carried everywhere during these disruptions.”
Avoid eating and drinking during flight
Experts encourage passengers to refrain from eating or drinking while on board. But if necessary, be brief. “If a passenger briefly removes his or her mask to eat or drink, other passengers in the vicinity should keep their masks on,” said a Harvard University report on COVID risk mitigation on planes.
Each moment a face mask is removed on the plane — including eating and drinking during a flight — the risk of infection increases. The longer a passenger eats, the greater the risk of infecting someone, said epidemiologist Ulrichs.
Does using the aircraft’s toilet increase the risk of exposure?
Much of this depends on passengers’ hygiene. The aircraft’s lavatory is ventilated, but it’s worth keeping in mind that you don’t know the hygiene of the previous occupant, including whether they wore a face mask, said Ulrichs. If another passenger took off their face mask while in the lavatory, more aerosolized droplets have the potential to reach you. So experts urged wearing face masks when using the toilet.
A case study published in November 2020 found that one passenger on board an evacuation flight from Milan, Italy, to Incheon, South Korea, may have been infected while using the lavatory. Researchers found that six asymptomatic passengers had COVID-19 while onboard. The passenger who became infected while likely in the lavatory reported that she wore an N95 respirator the entire flight — except while using the toilet.
There are surfaces within the lavatory, beyond the toilet itself, that may have been touched by other passengers, including the water tap and door latch, for example. “It’s unlikely, but possible, that the [COVID] particles could get on your hands — and then you could touch your face. So it’s also important to wash your hands. Using disinfectants is a good extra measure, avoid touching one’s face, and be mindful of cleaning after being in the bathroom so you can take measures that significantly reduce your risk,” Marcus said.
How can I best protect myself during a flight?
The use of face masks is highly emphasized (and in many cases required, like in Germany and the US) while at airports and on the plane. Some experts, like Marcus, go further, urging the use of two face masks to help ensure a proper seal around the nose and mouth.
Marcus recommended facing forward while seated and, again, avoid eating and drinking if you can. If you need to eat or drink, first check to see if the person next to you has their mask on. If not, politely request they put it on (or seek assistance from a flight attendant if they refuse).
Marcus also encourages passengers to keep their personal overhead vents, known as “gaspers,” on during the flight. His recommendation is backed by a study published in the Oxford University’s Journal of Travel Medicine that examined the risks of air travel during the pandemic, which said, “it is recommended that the gasper airflow be turned on to improve travel comfort, air quality and reduce person-to-person transmission of exhaled contaminants.”
Do I still need to take precautions if I’m vaccinated?
The CDC in early April updated its travel guidance to say that people who are fully vaccinated can travel at a low risk to themselves — noting that a person is only considered fully vaccinated two weeks after receiving the last recommended dose of vaccine.
Marcus is cautiously optimistic about the development. “We encourage people who are vaccinated to adhere to our recommendations because that combination can allow them to fly with high levels of confidence when they’re in the airport and when they’re on the plane itself.”
Vigilance is also necessary as variants continue to emerge and spread. In New Zealand, an airport worker became infected with the UK variant while cleaning a plane in Auckland. The employee was fully vaccinated, New Zealand officials said.
What else should I keep in mind while flying?
Protective measures should not be limited to only while in the air and at the gates, experts stressed. Consider the whole journey — including how you travel to and from the airports, and avoiding crowds at security queues, baggage claim, food courts, and concession areas. Be mindful of regulations in both the departing and arrival country, whether PCR tests are required before flying, and safety measures implemented at airports.
Experts, including the World Health Organization, also highlight the need for returning travellers to monitor their health upon their return for any potential symptoms, particularly because of the rising cases of COVID variants, to help reduce the spread of disease.