I was speaking with my neighbor the other day, whose age makes him both wise and at high risk should he contract COVID-19. I was wearing a mask — he was not. “Yeah, I don’t do that,” he said. I thought, “He must not understand how the COVID-19 virus is transmitted, because if he did, I think he would wear a mask.”
He went on to say, “The science around this changes all of the time, so who are you supposed to trust?” As a scientist, I am OK with some uncertainty as we learn more about diseases. For instance, it was believed that ulcers were caused by stress — now we know that they are largely an infectious disease. It’s the nature of scientific discovery that our “mental model” of how the world works evolves over time. The nature of how we understand COVID-19 is continuously evolving, which is normal and correct — and clearly frustrating.
When the pandemic began, scientists believed it was similar to influenza. We know a great deal about influenza. The last great pandemic involved influenza. It was a natural place to start. Influenza is spread by droplets, and COVID-19 is spread by droplets, so we deployed influenza-type strategies of hand washing and hygiene, wiping down surfaces, social distancing, etc. When that wasn’t enough, we used more draconian measures that included stay home orders and closing all but essential businesses.
Now we understand how COVID-19 is not like influenza; let me explain.
COVID-19 seems to fit the “eighty-twenty rule” of biology. 80% of the disease is caused by 20% of the transmission. Here’s how that 20% works with this virus.
Imagine a keyhole, and only a specific shape can fit through that hole. The COVID-19 virus has a specific shape and must land on a specific keyhole to pass through the lining of your nose, mouth, or lungs and into your bloodstream. These keyholes are spread out randomly. So, it takes multiple hits for a virus to infect you. If you are peppered with enough virus, eventually one will land on the keyhole, pass through and cause an infection. The total volume of virus that peppers your system is the key. How much time you are in contact with an infected person and the time sharing their air determines if you will contract COVID-19.
Both COVID-19 and influenza are transmitted via droplets. But unlike influenza, the droplets that remain suspended in the air are what matter most. Influenza is all about big droplets that land on surfaces, which we touch, and then carry up to our mouths, or eyes. COVID-19 is about small droplets that remain floating in the air that we share.
Imagine your tonsils as the breeding ground of the COVID-19 virus. Anything that pushes air past the tonsils will collect and expel virus. Singing, yelling, breathing hard, coughing, all will generate large droplets filled with virus. Talking or just breathing release small virus-containing droplets. The big droplets contain lots of virus but fall to surfaces within 6 feet — and yes, you could contract the virus from those surfaces, but it is difficult. Very small droplets float around for a long time, but don’t contain many viruses, and aren’t that infectious.
So, what about medium sized droplets? Medium sized droplets carry medium volumes of virus. And here is the key: medium sized droplets float around long enough to start to evaporate off their water. As the water evaporates, they turn into small droplets that can float around all day. But instead of carrying just a small volume of virus, these dried-out medium-sized droplets contain a medium volume of virus. They become concentrated “super-infectors.”
Outside, humans don’t share much air. Floating droplets dissipate, and we are all pretty safe. Inside, with minimal air movement, we share a lot of air, and receive multiple hits from virus-laden droplets. Thus, carpooling with extended family for celebrations like birthday parties, or even gathering in someone’s living room for a memorial service, with singing and sobbing, are more dangerous.
This is why wearing a mask is so important. I must confess that at first the whole universal masking thing made no sense to me. As a physician I have been trained to use a mask in a very specific way to avoid transmitting something like tuberculosis from one patient room to another when working in a hospital. Universal masking violates my medical training. So how could it work?
In China and Italy and New York City — all of the hotspots — the curves finally started to bend only after universal masking was imposed. Why?
Masks, even cloth masks, retain the biggest droplets and those nasty medium sized droplets. Only the small droplets that aren’t very infectious can get through. When an infected person wears a mask, and remember that you are most infectious before you even start to feel sick, the total volume of virus floating around in the air that we share is dramatically reduced. Because 80% of infections come from droplets floating around in the air, the simple act of wearing a mask is enough to stop the pandemic spread. How I wish we had known that in March.
It turns out that in COVID-19, masking is the next best thing to a vaccine. And probably nobody reading this will receive a vaccine before June of 2021.
Many say, “You cannot make me wear a mask.” That is true, but why wouldn’t you want to? You wear a mask to protect those around you, to beat the pandemic, to keep the economy open. Just like not smoking in restaurants or speed limits — they exist as public health interventions that make sense. I hope with a better understanding of how COVID-19 is transmitted, wearing a mask will make sense too.
Don’t stop washing your hands and don’t start touching your face. You can still contract COVID-19 from droplets on surfaces.
80% of COVID-19 appears to be transmitted through the air — the air you share.
Masking during COVID-19 is the next best thing to a vaccine.
Dr. Malcolm Butler is the chief medical officer at Columbia Valley Community Health and the health officer at the Chelan Douglas Health District in Central Washington.