We now know that masks have an effect on slowing the spread of COVID-19. Masks protect the wearer and the people around them, a two -way protection. We are going to explain in this article that widespread mask-wearing is a powerful way to extinguish an epidemic. (with some little math).
When a person exhales they spray out saliva particles mixed with viral particles. This virus-laden saliva spray is the main way that COVID-19 spreads.
When a contagious person breathes, they spray out roughly a thousand viral particles every minute. When they talk, they spray out roughly ten thousand viral particles every minute. When they cough, they spray out roughly a hundred thousand viral particles. And when they sneeze, they spray out roughly a million viral particles. The more viral particles travel from person to person, the higher the chance of infection.
MASKS ARE TWICE EFFECTIVE
Let us assume that a contagious person wears a 50 percent effective mask. That is, wearing this mask cuts in half the chance that they will infect a near-by susceptible person.
If both the contagious person and the susceptible person wear a mask, the first mask cuts the chance of infection by half, and the second mask once again cuts the chance of infection in half. So when both people wear masks, the chance of infection is half of half, which is 25%. That is a 75% drop in the chance of infection. Hence the double protection makes 50% effective masks to reduce infection risk by 75%.
We will move from two persons to the whole population. Let us assume that 50% effective masks are worn by 50% of the population (not all wear masks, and not all wear them properly).
Possible cases in the population:
1. No one wears the mask, the drop in disease transmission is 0%.
2. Only contagious persons wear the mask, the drop in disease transmission is 50%.
3. Only susceptible person wears the masks, the drop is again 50%.
4. All are wearing a mask, the drop in transmission will be 75%.
If only 50% of the population wears the masks, all the above cases are equally likely to happen. So we will take an average of all the four cases.
Average drop in disease transmission = 0+50+50+75/4= 43.75%
How to stop the epidemic?
We put out a fire by starving of oxygen. That is what we do when we douse the fire with water, sand, and foam. But you do not need to get rid of all the oxygen, you only need to reduce it enough to stop the fire from growing. The same approach can be adopted in an epidemic. If you lower the disease transmission rate just enough to stop the disease from spreading, you can douse the epidemic fire.
What is 'just-enough?' What is that magic number? We have calculated. If 50 % effective masks are worn by 50% of people, the average drop in disease transmission is 43.75%. This is not at all enough. But calculations tell us that if 60% of people wear 60% effective masks, disease transmission drops by 60%- which is just enough to stop the spread of COVID-19.
Hail the masks.
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