While masks are not a panacea for controlling the COVID-19 pandemic, there is mounting evidence that they are a useful tool for slowing community transmission of the disease. Researchers at the Centers for Disease Control and Prevention (CDC) took advantage of a natural experiment in Kansas, producing an analysis of mask efficacy after some counties enacted a mask mandate and others did not.
On July 2, Kansas Gov. Laura Kelly issued an executive order requiring people to wear face coverings when entering any indoor public space, visiting health care facilities, or using public transportation. State law, however, authorizes counties to issue public health orders that are less stringent than statewide executive orders. Many counties opted out of Kelly's mask mandate.
During the period of the CDC study, 24 counties adopted a mask mandate whereas 81 counties did not. The researchers then compared what happened to the COVID-19 incidence trends in counties with and without mandates. They reported that in early June, a month before Kelly's order, the daily average COVID-19 incidence rate in counties that would eventually adopt a mask mandate was three cases per 100,000. In counties that ultimately chose not to mandate masks, the daily incidence rate was four per 100,000.
By early July, in the week just after Kelly's mask order, the COVID-19 incidence rate had risen to 17 cases per 100,000 in the counties that would ultimately adopt the mandate—a 467 percent increase from early June. In the counties that would not adopt the mask order, there had been a 50 percent increase, for an incidence rate of six cases per 100,000.
By mid-August, the 7-day rolling average COVID-19 incidence had decreased by 6 percent to 16 cases per 100,000 in mandated counties. In non-mandated counties, it had increased by 100 percent to 12 cases per 100,000.
"After implementation of mask mandates in 24 Kansas counties, the increasing trend in COVID-19 incidence reversed," noted the researchers. "Although rates were considerably higher in mandated counties than in non-mandated counties by the executive order, rates in mandated counties declined markedly after July 3, compared with those in non-mandated counties. Kansas counties that had mask mandates in place appear to have mitigated the transmission of COVID-19, whereas counties that did not have mask mandates continued to experience increases in cases."
The Kansas jurisdictions with the greatest increases in COVID-19 cases were the ones that moved most quickly to require people to wear facial coverings while in indoor public spaces. It appears that those communities learned hard lessons early, ones that other Kansas localities are only now beginning to understand. Since August—as COVID-19 cases have risen steeply in the Sunflower State—the number of counties adopting mask mandates has now more than doubled to 50.
However, the current statewide COVID-19 daily incidence rate of 96 cases per 100,000 people three months after the study's cutoff date clearly shows that wearing facial coverings alone does not stop the transmission of the virus.
Setting aside authoritarian concerns over mandates, the data from the study indicate that wearing facial coverings will help mitigate the transmission of the disease. This could prove especially useful as more people crowd together indoors with the onset of cold winter weather. Despite the pandemic fatigue that we are all suffering, the CDC researchers remind us that "community-level mitigation strategies emphasizing use of masks, physical distancing, staying at home when ill, and enhanced hygiene practices can help reduce the transmission of [the COVID-19 virus]."