Mask wearing and frequent cleaning in planes help keep the virus from spreading.

The risk of COVID-19 transmission onboard a plane is “reduced to very low levels,” Harvard researchers concluded. The onboard ventilation systems coupled with measures such as masks, frequent cabin cleaning, and distancing during boarding and deplaning help keep the virus from spreading.

“This layered approach reduces the risk of SARS-CoV-2 transmission onboard aircraft below that of other routine activities during the pandemic, such as grocery shopping or eating out,” the report stated.

The Aviation Public Health Initiative (APHI), comprised of faculty and scientists at the Harvard T.H. Chan School of Public Health, published its Phase One report Tuesday, analyzing “gate-to-gate travel” onboard planes. It has not been peer-reviewed.

The initiative is sponsored by major U.S. airline lobbying group Airlines for America, along with other aircraft and equipment manufacturers, airline and airport operators. But the APHI insists its findings and recommendations are the “independent conclusions” of the Harvard researchers.

There have only been 13 peer-reviewed studies surrounding COVID-19 transmission on aircrafts.

“While investigation of the virus and its transmission is ongoing,” researchers said, “the research to date indicates a relatively very low risk of acquiring SARS-CoV-2 while flying.”

Three studies published in the Centers for Disease Control and Prevention’s journal of Emerging Infectious Diseases found likely cases of COVID-19 transmission onboard international flights, but they occurred before airlines implemented mandatory mask requirements.

The virus’ long incubation period combined with the lack of contact tracing limits the amount of data researchers can analyze surrounding transmission on planes.

“Until there has been widespread vaccination, there remains the risk of infection in all walks of public life,” the report said. “As with any activity during this pandemic, the choice to fly is a personal one and depends on a traveler’s health assessment, individual risk tolerance and the potential consequences of becoming infected.”

The APHI plans to release its Phase Two report in two months, which looks at “curb-to-curb” travel and analyzes risks associated with one’s time spent at the airport.

ABC News’ Dr. Leah Croll contributed to this report.