Face masks greatly reduce risk of COVID-19: Watch this video to see how

No measure by itself completely prevents the virus, but now there's evidence that face masks, social distancing and eye protection greatly reduce risk.
/ Source: TODAY

The key elements to reducing the spread of the coronavirus involve social distancing, proper hand hygiene and wearing face masks when you can't social distance. Yet there are still people who refuse to wear masks to help slow the spread of COVID-19.

NBC News investigative and consumer correspondent Vicky Nguyen demonstrated on TODAY how effective face masks truly are: She coughed onto petri dishes wearing three different types of face masks (cloth mask, a common surgical mask and an N95 mask) and after 60 hours, there was no bacteria growth developing on the dishes.

Research supports this idea, which is why face masks are encouraged when social distancing measures cannot be observed. Last month, a first-of-its-kind study, published The Lancet, took a comprehensive look at measures used to slow the spread of this pandemic, as well as other coronaviruses, including SARS and MERS. It analyzed 172 studies from 16 countries and six continents.

While many of its findings, which support the efficacy of face masks, social distancing and eye protection, are already recommended by public health officials, this research is important because it replaces "anecdotes" with evidence-based "clarity," study co-author Dr. Derek Chu, a clinical scholar of medicine at McMaster University in Ontario, Canada, told TODAY.

"Even though people have made conjectures about, 'Should we wear a mask?' ... the problem has been that uncertainty," he said. "CDC is saying wear a mask, but other people have countered that very rapidly, saying, 'It's more harmful than good.'"

Face masks greatly reduce transmission rates

The study looked at three measures separately: face masks, social distancing and eye protection.

To start, it found that, without a mask, social distancing or any other preventive measures, the risk of transmitting the coronavirus is 17.4%. Add a mask or respirator, and that number drops to 3.1%.

Based on the studies included in the latest research, Chu said the most effective types of masks were surgical masks or cotton masks with 12 to 16 layers of fabric.

He added, "Respirators are best used in the health care setting because they’re uncomfortable to wear, and if you’re not going to wear it properly, then it defeats the purpose."

Social distancing is the most effective strategy

One of the main takeaways from the research, per Chu, is that "physical distancing is highly effective, and every inch counts."

With less than a meter of distance and no other protective measures, the research found the risk of transmission was 12.8%. With more than 1 meter of distance, it's 2.6%.

"Two meters is even more effective, quite likely," Chu said.

He also called attention to the 6-feet rule that's become a way of life during the pandemic. Given that there's no definitive distance that eliminates transmission risk, Chu said he believes that 7 feet would be a more effective policy recommendation because it's more than 2 meters.

"That could half the risk of infection even further," he explained. "In high-risk situations, obviously, the further away from an individual, the better, if that person actively has an infection."

Eye protection offers benefit with little risk

Eye protection isn't a standard recommendation in the same way as face masks, in part because experts believe it's not the main way the coronavirus is transmitted. (The current school of thought is that it's droplets getting into the mouth and nose.)

The Lancet study found that rates of transmission dropped from 16% without eye protection and no other measures to 5.5% with eye protection, specifically face shields and goggles.

"The data says quite clearly and consistently, wearing eye protection is associated with a 5-fold reduction in transmission," Chu said. "Having that barrier would help prevent our hands touching our eyes, and it's also a barrier against the virus."

The overarching message from the research is that "no single intervention on its own made an individual completely impervious to transmission," he added. "We can’t neglect basic measures such as hand hygiene."