In this Jan. 5, 2022, file photo, students from Regional School Unit 5 wear COVID face coverings as they head home on a school bus in Freeport. Credit: Robert F. Bukaty / AP

Rural counties that enacted mask mandates saw fewer COVID-19 cases than nearby counties without mandates, a new study found.

The results support longstanding recommendations from public health officials that masking reduces the likelihood of virus transmission. It came as Maine towns continue to debate mask policies, although Gov. Janet Mills looks unlikely to reinstate a statewide mandate and hospitalization data suggest the virus may be on the decline here now.

The study from researchers in Kansas and Missouri and published in the Journal of Osteopathic Medicine looked at COVID-19 cases across 38 rural counties in Missouri, Iowa, Tennessee and Florida, half of which implemented mask mandates. It found in the month after counties enacted mask requirements, cases were 16.9 percent lower than in counties without mandates.

“These data support the effectiveness of mask mandates in reducing SARS-CoV-2 infection spread in small US counties where the population density may be less than in urban counties,” the authors concluded.

The study’s data were collected between July and October of 2020. That predates the more contagious delta and omicron waves, as well as the introduction of vaccines. It also covers a period when cloth masks were recommended for the general public. They are now considered less effective than medical-grade masks.

It is not the first study to find that mask mandates  reduced virus cases. But the research is notable because of its focus on less populous counties, as some speculated at the onset of the pandemic that lack of population density would itself impede the virus without the need for other public health interventions.

Maine was among the rural states to enact a mask mandate early on in the pandemic. The statewide mandate ended here last May after vaccines became widely available for all adults, although masks are still required in many schools. But the debate about mandatory masks has continued this winter as the virus has surged.

Maine officials said last fall that they supported U.S. Centers for Disease Control and Prevention guidance that recommends universal masking in counties with more than 50 cases of the virus per 100,000 people per week, but did not plan on enacting another mandate. All Maine counties remain significantly above that threshold.

Portland enacted its own mask mandate in early January, citing rising cases, while the town of Falmouth recently rejected a similar mandate.