SARS-CoV-2 Transmission On Commercial Airliners – An Epidemiologist’s View

The Blogosphere has had no shortage of posts from bloggers, including yours truly, pontificating on the risks of air travel during the Covid-19 pandemic. I have tried to supply readers with my understanding of various studies and other sources that have looked at this issue. And I’ve stated that my views should be taken with a grain of salt because I obviously have no education, training or experience in the field of epidemiology, immunology or any other field of medicine or public health.

At long last, I found and am sharing an article by a bona fide epidemiologist that provides a fairly easy to understand explanation of what scientists know about the spread of SARS-COV-2 on commercial passenger jets. The article is written by Dr. Katelyn Jetelina, Assistant Professor in the Department of Epidemiology at the University of Texas Health Science Center. She has a masters degree in public health and a PhD in epidemiology and biostatistics.

Please read the article here. It is a quick read. Some of the key findings are: (1) airplane HEPA filtration systems greatly reduce (but do not eliminate) the risk of transmission from airborne SARS-CoV-2 aerosols (droplets are another matter) but these systems often are not operating during boarding, taxiing, and disembarking; (2) proximity to an infected individual matters a lot; and (3) masks help and the more masks the better.

Proximity Matters

The article discusses a study of a flight from London to Vietnam in March 2020.

Because modes of transmission differ, scientific studies have shown that proximity to the index case (i.e., person originally infected before boarding) on a plane impacts risk of infection during a trip. A very extensive study traced all 217 passengers and crew from a 10-hour flight from London → Vietnam in March 2020. At the time, masks were not mandatory nor widely used. The index case was in business class and symptomatic (fever and cough). The scientists found 16 cases were acquired in-flight (i.e., secondary cases), 12 of which were in business class. This equated to a 75% attack rate in business class. Two cases were in economy class and another case was a staff member.” (Emphasis added)

Passengers in business class are not packed as tightly together as people in the economy cabin.

Masks Help

All other factors equal, masks reduce transmission… period.  A full aircraft is more dangerous than one with a light passenger load.  The longer the flight, the greater the risk of transmission.  The article states:

In a scientific review of studies early in the pandemic, two public health reports extensively assessed transmission rates in the presence of rigid masking. The results affirmed low transmission with masking:

• The first flight had 25 index cases but only 2 secondary cases. One of which was seated next to a row with 5 index cases.

• On 5 Emirates Airlines (served food onboard) flights with more than 1500 passengers found no secondary cases identified despite 58 index cases

A great modeling study was published in 2021 with a few very interesting findings, too:

• During a 2-hour flight with no masks, the average probability of infection was 2%. But if one sat next to an index case, the probability rose to 60%.

• During a 12-hour flight with no masks, the average probability of infection is 10% (or 1 in 10). If one sat next to an index case, the probability rose to 99%.

  • If everyone wore high efficiency masks the whole time, the probability was reduced by 73%. If everyone wore low efficiency masks, the probability was reduced by 32%.

  • If face masks were worn by all passengers except during a one-hour meal service, the probability was decreased by 59% (high efficiency masks) or 8% (low efficiency masks).”

A surprise

The article contained on finding I wasn’t expecting. Evidence leads to the conclusion that persons in window seats have a higher risk of contracting an infection in spite of the fact that they have fewer contacts with other passengers. That is the opposite of what I had assumed.

Final Thoughts

A major problem in dealing with the pandemic is the lack of clear and consistent direction from the scientific community. There is much about the virus that medical and public health officials don’t know. But based on scientific studies like the ones referred to in the article, the expert consensus is that wearing a good facemask on airplanes will reduce Covid-19 spread. When I take a domestic flight tomorrow, I will wear a KN95 mask onboard and in the airport.

In addition, today I’ll take one of the eight free rapid antigen Covid self tests the government mailed to U.S. households that requested them to see if I test positive. If the result is positive, I’ll take a PCR test to confirm or invalidate that result. I won’t travel with Covid for the sake of others and to avoid the possibly becoming sick away from home.

Happy and safe traveling!