So how well do masks protect against COVID?

published Apr 23, 2021, last modified Feb 01, 2022

Turns out, according to the CDC, very little.

Reposted with permission.

Instead of cherry-picking death rates without controlling for known large-magnitude age, ethnic and socioeconomic stratifications, refer to the March CDC study which found that mask mandates, even with uncontrolled epidemiological confounders, resulted in an average 0.5% decrease in the daily case growth rate (r) after implementation (paper mirrored here).

To put that in context, you can see from other data that during an epidemic wave, daily case growth rates are commonly large double-digit percentage increases (divide the weekly growth rates shown by 7).

Due to a government disinformation campaign about the airborne nature of the virus (likely intentionally waged to protect N95 mask supplies), virtually all of the state-level mask mandates in the US were put into place after the first epidemic wave had already ended. Despite the small magnitude apparent beneficial effects in the CDC study period (between the two waves), no state with a mask mandate escaped a large magnitude second epidemic wave.

Since states with mask mandates usually were also states with lockdown policies (since both policies depend on prevailing attitudes towards personal autonomy that would permit invasive state-based NPI measures), when the data is analyzed those states will turn out to have fared even worse in the second wave by forcing people 1) indoors near each other 2) away from sunlight and 3) fresh air and even 4) creating evolutionary selection pressure for more infectious lockdown variants which adapt to the need to jump the "air gaps" between the permitted lockdown "bubbles" in order to survive and propagate.

If mask mandates require the same prevailing permissive attitudes towards state-based NPI measures that also enable governments to execute economic lockdowns, then any attenuating effects of successfully enforcing a mask mandate is almost certainly canceled out by the aggravating effects of the latter, if not lost entirely relative to the case and death growth rates typically seen in waves.