ATLANTA — Keeping middle seats empty on airplanes could sharply reduce passenger exposure to the coronavirus that causes COVID-19, according to study results released Wednesday by the Centers for Disease Control and Prevention.

But most major U.S. airlines aren’t restricting access to those seats. And the last major holdout, Atlanta-based Delta Air Lines, earlier announced it will open up middle seats on flights starting May 1. A Delta spokesman reiterated Wednesday its plans have not changed.

Using modeling based on earlier lab studies at Kansas State University, the CDC found that aerosol exposures were reduced by 23 percent to 57 percent when middle seats were vacant compared to full flights. The tests used a surrogate virus.

However, because some of the research was based on work done before the pandemic, the results don’t account for the impact of U.S. airline passengers wearing masks, which they are required to do except when eating or drinking. Also, the studies looked at exposure, rather than actual virus transmission.

The researchers wrote that other studies indicate that masks do not seem to eliminate all exposure to viruses via droplets or aerosols. “Combining the effects of masking and distancing is more protective than either by itself,” they wrote.

The news comes as air travel has picked up and many Americans contemplate vacations for the year ahead, emboldened by vaccinations. Delta alone lost more than $12 billion last year after passenger traffic collapsed industrywide.

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Industry association Airlines for America, which represents Delta among others, on Wednesday highlighted safety measures already in place for flights, such as mask mandates, passengers filling out health forms, increased disinfection measures and sophisticated ventilation systems.

“Multiple scientific studies confirm that the layers of protection significantly reduce risk, and research continues to demonstrate that the risk of transmission onboard aircraft is very low,” the association wrote in an emailed statement.

Still, questions have lingered about having lots of people sitting near each other on jets, potentially for hours. There are competing views about the risks.

CDC guidelines already recommend against travel for unvaccinated people. Since January, the federal government has mandated mask wearing for everyone on planes. And, fearing a post-Easter surge of COVID-19 cases, the CDC’s director recently urged people to “limit travel to essential travel for the time being.”

Delta’s pandemic-related policy of keeping middle seats clear was a way to distinguish itself from competitors, who had dropped such restrictions months earlier. In so doing, there were indications it could charge a premium for its seats.

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But in announcing plans to end that policy, Delta CEO Ed Bastian wrote in late March that “with vaccinations becoming more widespread and confidence in travel rising, we’re ready to help customers reclaim their lives.”

Keeping middle seats clear effectively eliminated about a third of the airline’s available seats.

Delta did assign some passengers to middle seats during the Easter travel period as it grappled with staffing challenges that caused it to cancel some flights.

Story Filed By Cox Newspapers

For Use By Clients of The New York Times News Service