NEW YORK (NYTIMES) - Keeping the middle seats vacant during a flight could reduce passengers' exposure to airborne coronavirus by 23 per cent to 57 per cent, researchers reported in a new study that modelled how aerosolised viral particles spread through a simulated airplane cabin.

"Farther is always better in terms of exposure," said Mr Byron Jones, a mechanical engineer at Kansas State University and co-author of the study. "It's true in airplanes, it's true in movie theaters, it's true in restaurants, it's true everywhere."

But the study may have overestimated the benefits of middle seats, because it did not take into account mask-wearing by passengers.

"It's important for us to know how aerosols spread in airplanes," said Dr Joseph Allen, a ventilation expert at Harvard T.H. Chan School of Public Health who was not involved in the study.

But he added, "I'm surprised to see this analysis come out now, making a big statement that middle seats should stay open as a risk-reduction approach, when the model didn't include the impact of masking. We know that masking is the single most effective measure at reducing emissions of respiratory aerosols."

Although scientists have documented several cases of coronavirus transmission on planes, airplane cabins are generally low-risk environments because they tend to have excellent air ventilation and filtration.

Still, concern has swirled around the risk of airplane travel since the pandemic began. Planes are confined environments, and full flights make social distancing impossible. Some airlines began keeping middle seats vacant as a precaution.

The new paper, published on Wednesday (April 14) in the Morbidity and Mortality Weekly Report, is based on data collected at Kansas State University in 2017.

In that study, the researchers sprayed a harmless aerosolised virus through two mock airplane cabins. (One was a five-row section of an actual single-aisle plane; the other was a mock-up of a double-aisle wide-bodied plane.) The researchers then monitored how the virus dispersed through each cabin.

For the new study, researchers from Kansas State and the Centres for Disease Control and Prevention used the 2017 data to model how passengers' exposure to an airborne virus would change if every middle seat remained open in a 20-row single-aisle cabin.

Depending on the specific modelling approach and parameters they used, keeping the middle seats vacant reduced the total exposure passengers experienced in the simulation by 23 per cent to 57 per cent, compared with a fully occupied flight.

"Some airline carriers have been operating with a vacant seat policy, and this study supports the effectiveness of that intervention, in the context of other measures that are in place," a CDC spokesperson said in an e-mailed statement.

This reduction in risk stemmed from increasing the distance between an infectious passenger and others, as well as from reducing the total number of people in the cabin, which lowers the odds that an infectious passenger would be aboard in the first place.

The laboratory experiments on virus dispersal in aircraft cabins were conducted several years before the current pandemic began and did not account for any protection that wearing masks could provide.

Masking would reduce the amount of virus that infectious passengers emit into the cabin air and would likely lower the relative benefit of keeping middle seats open, Dr Allen said.

Mr Jones concurred. "In general, I would think that wearing a mask would make this effect much less pronounced," he said.

He also noted that simply being exposed to the virus does not mean that someone will be infected by it.

"The extent to which exposure reduction might decrease transmission risk is not yet understood," the CDC spokesperson said.

The cost-benefit analysis is tricky for airlines. But purely from a health perspective, keeping middle seats open would be helpful, providing a buffer between an infectious person and others nearby, according to Dr Alex Huffman, an aerosol scientist at the University of Denver who was not involved in the study.

"Distance matters, for both aerosols and droplets," he said.