(CNN) -- Leaving middle seats vacant on airplanes can significantly reduce a passenger's risk of being exposed to the coronavirus that causes Covid-19, a new study suggests.
The risk of being exposed to the virus may be reduced by 23% to 57% on single-aisle and twin-aisle aircraft when middle seats are vacant compared with a full occupancy flight, according to the study published on Wednesday by the US Centers for Disease Control and Prevention.
Researchers from the CDC and Kansas State University used laboratory models to simulate how much exposure to virus particles could be reduced when middle seats are kept vacant in an aircraft cabin.
The models were based on the spread of bacteriophage aerosols used as a surrogate to estimate the airborne spread of the coronavirus. Bacteriophages are viruses that can infect bacteria. The analysis did not measure the impact of wearing masks, which is currently required on flights, but the researchers noted that some virus aerosol can still be emitted from an infectious masked passenger and so distancing could still be useful.
The models suggested that, with vacant middle seats, risk reduction ranged from 23%, which was observed for a single passenger who was in the same row but two seats away from an infectious passenger, to 57%, observed when middle seats were vacant across a section of three rows containing a mix of people with Covid-19 and other passengers.
"When the infectious and other passengers who would have had middle seats were removed, leaving six infectious passengers out of 12 total passengers remaining in the window and aisle seats, a 57% exposure reduction was observed," the researchers wrote in their study.
Overall, "it is important to recognize that the current study addresses only exposure and not transmission," the researchers wrote. More research is needed to determine the risk of the virus possibly being transmitted and causing illness.
Recent update to travel guidance
Earlier this month, the CDC said fully vaccinated people can travel at low risk to themselves, but travel still isn't recommended because of rising numbers of coronavirus cases.
The agency said that as long as coronavirus precautions are taken, including mask wearing, fully vaccinated people can travel within the United States without getting tested for Covid-19 before or self-quarantining after.
For international travel, fully vaccinated people don't need a Covid-19 test prior to travel -- unless it is required by the destination -- and do not need to self-quarantine after returning to the United States. They should still have a negative Covid-19 test before boarding a flight to the US, and a follow up test three to five days after their return, the CDC noted.
The CDC considers someone fully vaccinated two weeks after receiving the last required dose of the Covid-19 vaccine. The updated guidance does not apply to unvaccinated people. The CDC advises anyone who hasn't been fully vaccinated to continue to avoid travel.
All Americans, regardless of vaccination status, should wear a mask and practice public health measures such as physical distancing and washing hands frequently, the CDC says.
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