Do masks really work against COVID-19 for HCW? What does the science say?

Today’s question is slightly unrelated to physiotherapy, but at the same time very related! As everyone should know by now, masks will be mandatory at work.

Many Healthcare workers are currently wearing N95/KN95s or surgical masks.

So how much protection does a mask provide or… does it even provide any protection at all?

What does the science say?

1)    Study 1 demonstrates how much viral shedding can be reduced when you are using a mask. 

2)    Study 2 compares N95s to surgical masks.

Covid-19 and many other acute respiratory virus illnesses can be transmitted either through droplets and fine-particle aerosols. Although hand hygiene is always recommended along with physical distancing, these hygiene practices are not always possible.

Wearing a mask is a great mitigation strategy. Some believe that it gives you a sense of invulnerability. That idea is false speculation and unscientific. In fact, if you can teach someone how to wash their hands, you can definitely teach anyone how to properly wear a mask. 

Masks should be worn to prevent onward transmission (source control) and to protect the user (the wearer). 

FIRST STUDY

They screened 3363 individuals. 246 individuals provided exhaled breath samples. Half of the group were then randomized to NOT wearing a face mask during first exhaled breath collection and the other half were randomized to wearing a mask.

111 were infected by human coronavirus, influenza or rhinovirus. Some were infected by both coronavirus and influenza. These 111 were investigated in this study. 

They tested viral shedding, meaning viral copies per sample, in nasal swabs, throat swabs, respiratory droplets samples and aerosol samples. They then compared the latter two samples (droplet samples with masks and without masks).

Ultimately, viral shedding was highest in nasal swabs, much less in throat swabs. 

Viral RNA was also identified in respiratory droplets and aerosols for all three viruses:

Coronavirus: (30% droplets, 40% aerosols)

Influenza: (26% droplets, 35% aerosols)

Rhinovirus (28% droplets, 56% aerosols)

These concentrations of viruses were collected while NOT wearing a surgical mask. 

The findings?

Masks don’t protect from influenza as well as they do for coronaviruses. SHOCKING?… not really.

For coronavirus, wearing a mask REDUCES droplets and aerosols shedding significantly!

For the influenza, wearing a mask significantly reduces droplets ejection but NOT for aerosols.

Unfortunately, wearing a mask was not very effective for rhinoviruses…

What is most interesting about this study is that surgical face masks were effective in reducing emission of coronaviruses particles in BOTH forms (droplets and aerosols)!

Also, in general, the majority of participants did not shed detectable levels of coronavirus droplets or aerosols WITHOUT mask. So, with a mask, the odds of shedding the virus is even lower to a target.

Duration of shedding:

Breath collection were conducted for 30 mins.  

This may imply that prolonged close contact seems necessary for the transmission of COVID-19 to occur. Unfortunately, the study did not assess shedding through coughing. However, normally in real life, people do not cough directly on someone. It would be very impolite!

CERTIFIED masks ONLY when physical distancing isn’t possible!

SECOND STUDY

The second research was quite simple. They evaluated the odds of acquiring a viral respiratory infection for healthcare professionals wearing either a N95 or a surgical mask at various outpatient medical centers.

The results?

N95s were no better than surgical masks. Roughly 8% from each group caught the influenza.

N95s still seem to work better for aerosol though. But this was not mentioned in the article.

THE MATH, obviously based on the 2 studies only. In this study shedding of coronavirus was 30% without mask and 0% with mask. *based on a small sample size.

First study

(for droplets) N95 =KN95 = surgical mask =95% protection (based on the second study)

 (shedding coronavirus without a mask) = 30%

 (if you don’t wear a mask and they wear a mask) 30% * 0.05 & = 1.5 % chance of catching the virus.

 (if you wear a mask and they don’t wear a mask) 0.00 of 30 % = 0 chance of you giving it.

(if both wear masks): 0 * 1.5% = 0 % chance of catching it or giving it. 

 BOTTOM LINE

If you wear a mask and the person in front of you is also wearing a mask as well (N95/KN95 or surgical mask), no one should catch it through droplets or aerosol. 

Healthcare workers shoulder wear masks at work when physical distancing isn’t possible. Stats don’t lie. These masks WORK.

When in doubt, CLEAN YOUR HANDS WITH SOAP!

Physio Summum Brossard

Clean your hands with soap for 20 seconds! This KILLS coronaviruses

Reference:

1)    Nancy H.L.Leun et al. Respiratory virus shedding in exhaled breath and efficacy of face masks.Nature Medicine 26, 676-680 (2020).

2)    Radonovich LJ Jr. N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: Randomized Clinical Trial. JAMA 2019