Editor’s note: Last week, a Mountaineer reader asked that we cite studies that prove masks are even remotely effective in stopping the spread of any communicable virus. Because we’re a local newspaper who seeks out local experts, we tossed out the challenge to the Haywood County Public Health Department, and Dr. Mark Jaben, the county medical director, provided the following information.
A reader has asked for the scientific evidence that masks work.
Rest assured, I’ll get to the science in a bit. But I wonder the reason for asking — to rationalize not wearing a mask, or to influence others who choose not to? It is a choice, and that matters in how to apply the science.
Here is the straight scoop. Masks alone cannot completely eliminate exposure or infection. Face coverings do limit the amount of virus an infected person expels and the amount of virus a person might breath in.
Combining face coverings with the other public health recommendations-avoiding crowds, distancing, face coverings when you can’t, handwashing — reduces the viral load.
Viral load is the amount of virus your immune system has to fight off. The lower the load, the more likely your immune system can protect you. Exposure alone does not equal infection. The virus must not only get on you, it must get inside you.
If the load is small enough, the immune system can handle it. If the load is enough to overwhelm the immune system, you get sick. Long-lasting symptoms, serious illness and death happens when the immune system goes into overdrive, attacking normal cells too.
Wearing a mask does two things: it limits what an infected person expels into the air, limiting exposure to others, and limits what gets in you, limiting the load on your immune system. Face coverings are not the full answer; they do play a significant role in reducing the viral load and preventing illness.
So if you’ve learned enough, feel free to move on. If you want to hear more, keep reading.
A virus containing droplet is 5-10 microns in size. A virus is 0.125 microns — 10-40 times smaller. CO2 and O2 molecules are 150 times smaller yet. Here is a good explanation of particle sizes and mask effectiveness: https://www.fast.ai/2020/06/26/particle-sizes/
Virus is small enough to pass thru any material. But virus is not expelled into the air as isolated virus; it is contained in droplets or aerosols (read: snot and mucous), which are too big to pass thru the material.
Droplets are bigger than 5 microns; aerosols less than 5 microns. An N95 mask, for instance, blocks particles down to 0.3 microns. And, to get deep in the weeds, an N95 can block particles smaller than 0.3 microns because particles don’t move in a straight-line like water going through a sieve. They bounce around so are susceptible to getting caught in the weave of the fabric.
Depending on which material and how that material is constructed, face coverings, are 30-90% as effective as an N95.
So different materials filter droplets and aerosols differently, but each filters to some degree and remember, the goal is to reduce the viral load. Face coverings have their greatest benefit as source control — preventing the amount of virus laden particles an infected person expels into the air — in some studies as much as 95 percent.
Howard, J. et al; Face Masks Against COVID-19: An Evidence Review. Preprints 2020, 2020040203
Face coverings are less effective as PPE (personal protection) for the person breathing virus in from the air, but remember, the goal is to reduce the load and every little bit helps.
As you can also see, the even smaller size of carbon dioxide and oxygen molecules easily allow passage through any face covering material. Also, face coverings don’t form a perfect seal. So there is plenty of room for CO2 and O2 to freely move in and out, preventing buildup of CO2 or causing a low oxygen level. See video # 56- https://youtu.be/4cH0rpRlcJQ
Here is the biggest reason to wear a mask- the highest viral loads are expelled by an infected person a few days before symptoms start and before the person even knows they are infected, and the first few days of symptoms when it is unclear they might have COVID-19. By then others have been exposed to that highest viral load.
To date, of all the people who have tested positive in Haywood County, most often they were in places where they were not wearing a face covering continually, and most others around them weren’t either at work, family gatherings, restaurants, events or religious services.
In a hair salon in Missouri, two staff members were sick and coughing and continued to work, exposing 140 customers and seven other staff. None of the exposed people tested positive or got sick. They were all wearing a face covering.
I do hope this gives our reader some insight into the role that face coverings play in controlling this pandemic.