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(NEXSTAR) — The back-to-front boarding process, adopted by multiple major airlines amid the coronavirus pandemic, is “substantially worse” at preventing the spread of COVID-19 than the traditional method, according to a new study.

The study’s authors concluded that back-to-front boarding, as compared to more traditional pre-pandemic boarding processes, increases the risk of exposure by approximately 50%. And when compared to random boarding, back-to-front boarding roughly doubles the risk of exposure.

“Our results suggest that the new boarding procedures increase the risk of exposure to COVID-19 compared with prior ones and are substantially worse than a random boarding process,” reads a portion of the study’s abstract, published in the Royal Society Open Science journal.

Major airlines including Delta, JetBlue and United adopted the back-to-front boarding process amid the pandemic in 2020, in the hopes of minimizing instances of passengers needing to pass by each other in the aisles. But the study’s authors, who had previously studied the spread of Ebola on aircraft, found that back-to-front boarding results in increased instances of clustering as passengers wait for those who boarded previously to stow their luggage.

“Back-to-front boarding by rows is equivalent to one zone per row and can thus be expected to yield increased clustering and exposure to the virus,” the authors write.

The researchers, from Florida State University and the University of West Florida, further concluded that infection risk can be minimized by prohibiting travelers from using overhead bins at all, and boarding passengers seated by the window before those in the aisle. Keeping middle seats empty also “yields a substantial reduction in exposure” across different boarding processes.

Back-to-front boarding policies “do not improve on the old ones in any situation studied here,” they add.

Of the major U.S. airlines that adopted back-to-front boarding processes amid the pandemic, Delta Air Lines is the only carrier that still boards back-to-front. Delta’s current boarding policy is scheduled to remain in effect until April 30, according to the airline’s official website.