NNT is the number needed to treat to result in one positive outcome.
Stated another way, how many people need to wear a face mask to eliminate one new case or eliminate one mortality?
I ran some numbers on my County, a year ago, when the numbers were different. It seemed then that perhaps 10,000 to 50,0000 people needed to wear a face mask to prevent one bad outcome (which assumed that general population use of cloth masks, used incorrectly, had some positive effect). I have not run numbers for today.
The second question is, what is the efficacy of face masks in reducing the spread of the disease?
We say that vaccines are around 90+/-% effective in preventing Covid-19.
What is the efficacy of a face mask?
Considering numerous charts, like this one, the efficacy is likely low. The Czech Republic was – in March to May of 2020 said to prove that wearing face masks stopped Covid-19. But late in 2020, cases in Czechia rose to become amongst the worst in Europe.
At the right of the chart for Germany, the “Medical mask mandate” refers to an important change in Germany. Germany banned the use of cloth face masks and surgical masks and mandated the use of FP2 masks (equivalent to N95 masks in the U.S.). Even with an enforced government mandate to wear N95 masks, positive test cases rose sharply several weeks later.
Remember, I am a brain injured idiot who makes observations and asks stupid questions.
My stupid questions are:
- What is the NNT for face masks?
- What is the efficacy for face masks?