So Just How Effective Are Those Masks?

This article from The Annals of Internal Medicine appeared in my inbox this morning after being picked up by the National Center for Biotechnology Information/National Institutes of Health.

The question the authors wanted to answer was simple: Do surgical and cotton masks block the transmission of Covid-19?

The conclusion I found stunning - not only was the answer no (that didn't surprise me) but the outside of masks were more contaminated that the inside of face masks - counterintuitive right?

The study size was small: 4 patients and the study did not compare the use of these masks to N95 masks. Given that N95 masks are in short supply and a previous study showed that surgical masks were effective in preventing the dissemination of the influenza virus, the researchers wanted to know if surgical masks would also prevent the spread of Covid-19.

They had each of the patients cough 5 times on a petri dish that was 20 cm (approx 10 inches) away from their mouth. They coughed in this sequence: without a mask, a surgical mask, a cotton mask and then again without a mask.

The masks were swabbed in this order: the outside of the mask first then the inside side of each of the masks.

Here were the results: all surfaces on the outside of the masks were positive for Covid-19 whereas only one patient contaminated the inner and the outer surfaces of the surgical and the cotton masks.

So how is it that more virus was found on the outside of the mask - not the inside as one would suspect? Here's the reason postulated: Since the masks are not tight fitting, a turbulent jet of air is created at the edges of masks where the particles escape and essentially contaminate the outside of the surface. I think of it as a similar effect to how our glasses get fogged up and our breath rises up when we cover our nose and mouth.

But it doesn't explain the lack of virus on the inside of 3 out of 4 of the masks. As the authors noted, the velocity of the cough may have forced the particles straight through to the outer surface, but it doesn't account for larger particles coughed that would have been unable to penetrate.

Here's what the authors' say: "We do not know whether masks shorten the travel distance of droplets during coughing. Further study is needed to recommend whether face masks decrease transmission of virus from asymptomatic individuals or those with suspected COVID-19 who are not coughing.

In conclusion, both surgical and cotton masks seem to be ineffective in preventing the dissemination of SARS–CoV-2 from the coughs of patients with COVID-19 to the environment and external mask surface." 

Keep in mind that the authors were careful to point out that the study:

1. Did not include N95 masks.

2. Does not reflect the actual transmission of infection from patients with Covid-19 wearing different types of masks.

3. The study did not test whether masks shorten the travel distance of droplets during coughing. 

4. The study did not test if face masks decrease transmission of virus from asymptomatic individuals or those with suspected COVID-19 who are not coughing.

So there is still a lot more that would be helpful to know but for me, the takeaway is clear. Presuming my family and I don't have Covid-19, it still behooves us to:

• thoroughly wash our hands after removing a mask, 
• throw away disposable masks after single use or rewash the mask if it's reusable 
• continue to maintain social distancing

To read the full study, follow this link.