The Centers for Disease Control and Prevention (CDC) tried to extend the mask mandate—originally meant to expire on Monday—to early May because of concerns over the dominant BA.2 Omicron variant, which is leading to rising COVID cases in the U.S.

So how safe is it to get on a plane without a mask, or with a large number of unmasked passengers?

Airplane filtration

The airline industry argues that flying may actually be safer than other forms of indoor activity, like dining, in part owing to a plane’s high-grade filtration systems, which can remove droplets that carry the coronavirus. According to the International Air Transport Association (IATA), a plane’s filtration system renews air inside the cabin once every three minutes, which is roughly 10 times as frequent as air circulates in an office building.

But a plane’s effective filtration system leaves the danger of catching COVID from air that has not yet been filtered. For a passenger, that might come from contact with airborne droplets from someone close by, such as a neighboring passenger or someone traveling to and from different parts of the plane.

Planes also turn off their filtration systems during boarding and deplaning, as well as during refueling stops in transit. These periods are the points when most passengers are likely moving around the plane as they handle their luggage, which may increase the risk of transmission.

In addition, filtration systems may not be as good—if they exist at all—during other parts of the air travel process, such as when passengers line up on the jet bridge that connects the airport gate to the plane.

Do masks help prevent COVID spreading on a plane?

A mask serves two purposes: It prevents a COVID carrier from transmitting the virus to other people, and protects the wearer against catching COVID from someone else. Masks differ in terms of their level of protection, especially regarding more transmissible COVID variants like Omicron, with N95 masks providing the most and cloth masks providing the least protection.

Because of the difficulty of determining how and when someone on a flight may have caught COVID, we don’t have a clear picture of how easy it is to catch COVID on a plane. Yet some early studies suggest that masking on flights did help to prevent transmission, at least early in the pandemic. 

A September 2020 study found no cases of in-flight transmission on long-haul flights by Emirates—an airline with a strict masking policy—between Dubai and Hong Kong, despite there being positive cases on the flight among those who boarded.

Another study, from March 2021, estimated that allowing a one-hour meal service during a 12-hour flight—when you might assume most passengers would take off their masks to eat—increased the chance of infection by 59% compared with a scenario when masks were kept on during the whole flight.

However, these studies were conducted before the more transmissible Omicron variant emerged. In December, the chief medical adviser to the IATA estimated that passengers were two to three times as likely to catch Omicron on a plane as compared with earlier COVID variants.