Why are masks so ineffective, even if we presume that they are effective? Because almost everybody that is wearing them does not have COVID-19. So in those people, there is no chance that they could provide any benefit, regardless of how effective they are.
Last summer I did a “number needed to treat” (NNT) calculation to prevent one new case and one death. Using the County numbers in effect at the time, and assuming masks were 100% effective and that no other mitigations (e.g. social distancing) were in use:
- 1,000 people would need to wear a face mask to prevent one new case of Covid-19
- Between 50,000 and 100,000 people would need to wear a face mask to prevent 1 additional death in my county.
Because face masks are treatment for the almost exclusively healthy who do not have Covid (and masks were to provide outbound protection, and virtually no inbound protection), they were an extremely ineffective way to fight a virus.
In the real world, masks were not 100% effective – some studies found them to be 0%, some perhaps 10-20%, and one CDC study found them to be perhaps 1-2% effective. When you throw those into the calculation, the overall effectiveness in the entire population – assuming 100% “Compliance”, is nearly zero percent.
If 1,000 people wore masks which, using the CDC’s reported number, were 2% effective, than 50,000 people had to wear a mask to prevent 4 cases. In my County, with just under 200,000 population and daily cases of 50 to 100 per day, at best, perfect mask usage might prevent 4 new cases.
If we compared this County with an identical County not wearing face masks, we would then see there 54 to 104 cases per day. If we draw these epicurves on the same chart, we see there is essentially no difference in cases between the two counties.
(Note – except for the 50-100 new cases values, which are real world data, all other values are based on assumptions and a simple model. Real world numbers will vary from this. This is a model, not reality.)
If properly fitted N95 masks, used properly and replaced often, were used, we would have seen inbound protection. However, the CDC ordered us not use N95s or certified surgical face masks and said we should use random bits of cloth, using random designs, assembled by person of unknown skill. Couple with extensive re-use without frequent changes and re-washing, these masks were likely useless.
This explains why it is that well after we had high compliance mask mandates in effect, daily new positive tests great by a factor of 10x or more. By the end of January, studies estimated 30% to 55% of persons in California (estimates varied by county) had anti-bodies to Covid-19. Which means the mitigations in effect – and California was considered among the strictest in the nation – had little or no effect.