Is it safe to fly with the coronavirus still circulating? That depends partly on where you are. But while hard evidence is scarce, it appears the risk of being infected with the coronavirus during a flight is relatively low.
“Overall, planes are probably safer than poorly ventilated pubs, where similar densities of people do not wear masks and talk a lot and loudly,” says Julian Tang at the University of Leicester in the UK.
It is of course safest not to travel, especially if you are vulnerable. And if you have symptoms that might be coronavirus, you definitely must not travel.
Walking, cycling or travelling in your own vehicle minimises the risk of coming into contact with people who might be infected. If you use public transport, the risk depends firstly on the odds of an infected person being on the same bus, train or plane, and then the odds of them infecting you.
Travelling in South Korea, for instance, where just 1 in about 225,000 people test positive every day, is inherently safer than travelling in the US, where 1 in 6500 people test positive every day. In the UK, 1 in 60,000 people are confirmed positive daily.
If you sit on a plane near someone who is infected, how likely are you to catch the virus? We don’t know for sure as there is little to go on, but some case studies offer clues.
One describes a 5-hour flight from Singapore to China on 23 January, where 11 of the 325 people on board were infected by one man. Passengers were screened before boarding, but the man developed a fever during the flight and was not wearing a mask. It is not clear how transmission occurred.
However, when an infected couple flew from China to Canada on 22 January, none of the other 350 passengers on the 15-hour flight were infected. Masks were worn.
In a document on the medical evidence for in-flight transmission, the International Air Transport Association (IATA), an industry body, says that when four airlines followed up with 1100 passengers confirmed to be infected after flying, just one passenger may have been infected by one of them.
It’s not clear how reliable this finding is, however, as no details have been published and the IATA did not respond to queries. Nonetheless, there are reasons to think the risks are low.
Many airports check people’s temperatures before they board, and airlines now disinfect planes between flights and require passengers to wear masks. The air on planes is also replaced every 3 to 5 minutes, and the air that is recirculated goes through HEPA filters that should remove almost all droplets containing viruses.
“The ventilation systems on planes are very effective in reducing the overall concentration of any airborne pathogen exhaled by passengers,” says Tang. The main risk may be face-to-face conversations where air can be exchanged before being pulled away – along with any conversations before or after the flight.
In the US, the risk of infection is about 1 in 4000 if a flight is full, estimates Arnold Barnett at the Massachusetts Institute of Technology. If the middle seats are left empty, the risk falls to 1 in 8000.
For the UK, the equivalent risks are about 10 times lower, says Barnett. That is, there is just a 1 in 40,000 chance of infection. These are just rough estimates based on many assumptions, however.
It is not clear how travelling on trains or buses compares as their ventilation systems vary. For instance, the air on Eurostar trains is replaced every 15 minutes. Eurostar did not answer when asked if its trains have HEPA filters.
In China, a study of 2334 people who travelled on high-speed trains while infected concluded they infected 234 other passengers – but there were 72,000 people who sat within three rows of those already infected, and just 234 of them got infected too.
newscientist.com, 21 August 2020
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