TORONTO -- A new study has found that SARS-CoV-2, the virus that causes COVID-19, is evolving to get better at becoming airborne in its newer variant forms, raising concerns that loose-fitting face masks only provide "modest control" against infection.

The study, led by the University of Maryland School of Public Health, reports that the virus has moved towards "more efficient aerosol generation." Researchers say this means that public health measures will be needed to protect those in public-facing jobs and working indoors until vaccination rates are "very high."

Those measures include improved ventilation, increased filtration, UV air sanitation and tighter-fitting masks, in addition to vaccines.

The study was published Tuesday in peer-reviewed medical journal Clinical Infectious Diseases.

Results of the new study show that people infected with the Alpha variant expelled 43 to 100 times more virus into the air when they breathed than people infected with the original strain of the virus.

The study notes that this was the dominant strain that was circulating during the research period.

Don Milton, professor of environmental health at the University of Maryland, said the findings provide further evidence that transmission of COVID-19 is primarily airborne, spreading from the nose and mouth of an infected person by sprays of large droplets when in close proximity.

"We know that the Delta variant circulating now is even more contagious than the Alpha variant. Our research indicates that the variants just keep getting better at travelling through the air, so we must provide better ventilation and wear tight-fitting masks, in addition to vaccination, to help stop spread of the virus," Milton said in a press release.

Researchers found that the amount of airborne virus coming from Alpha variant infections was 18 times more than that of the amount of virus found in nasal swabs and saliva.

"We already knew that virus in saliva and nasal swabs was increased in Alpha variant infections," one of the study's lead authors and doctoral student Jianyu Lai explained in the release. "But our study shows that the virus in exhaled aerosols is increasing even more."

Researchers said that these increases in airborne virus from Alpha variant infections occurred before the Delta variant arrived in the U.S., indicating that the virus is "evolving to be better at travelling through the air."

To test how well masks work at preventing airborne spread, researchers measured how much COVID-19 is breathed into the air by infected patients and compared it to the amount of virus that is exhaled when they wear a cloth or surgical mask.

The study found that face coverings "significantly reduced" the amount of virus that is exhaled into the air from those infected with COVID-19 by about 50 per cent, but noted that loose-fitting cloth and surgical masks are unable to completely prevent virus particles from getting into the air.

Researchers said the study shows that a "layered approach" to virus control measures is "critical" to protect those returning to public work spaces.

"The take-home messages from this paper are that the coronavirus can be in your exhaled breath, [it] is getting better at being in your exhaled breath, and using a mask reduces the chance of you breathing it on others," Jennifer German, study co-author and assistant clinical professor at the University of Maryland, said in the release.