A study from the Centers for Disease Control and Prevention released Wednesday found that keeping planes’ middle seats free of passengers reduced the risk of exposure to COVID-19 between 23 and 57 percent in comparison to a packed flight, depending on the size of the jet. The majority of large U.S. airlines have, however, already been filling their middle seats for months as air travel slowly climbs towards pre-pandemic levels. As of late March, Delta was the only major carrier still blocking off middle seats, a provision that will last through April. The study, done in conjunction with Kansas State University, modeled planes full of unmasked passengers, though face coverings are currently required on flights. The CDC has said that fully vaccinated individuals are safe to travel.