CDC study finds small efficacy of face masks

How much reduction in the spread of Covid-19 comes from wearing face masks? 10%? 25%? 50%?

CDC study finds 0.5% to 1.8%:

During March 1–December 31, 2020, state-issued mask mandates applied in 2,313 (73.6%) of the 3,142 U.S. counties. Mask mandates were associated with a 0.5 percentage point decrease (p = 0.02) in daily COVID-19 case growth rates 1–20 days after implementation and decreases of 1.1, 1.5, 1.7, and 1.8 percentage points 21–40, 41–60, 61–80, and 81–100 days, respectively, after implementation (p<0.01 for all) (Table 1) (Figure). Mask mandates were associated with a 0.7 percentage point decrease (p = 0.03) in daily COVID-19 death growth rates 1–20 days after implementation and decreases of 1.0, 1.4, 1.6, and 1.9 percentage points 21–40, 41–60, 61–80, and 81–100 days, respectively, after implementation (p<0.01 for all). Daily case and death growth rates before implementation of mask mandates were not statistically different from the reference period.

Source: Association of State-Issued Mask Mandates and Allowing On-Premises Restaurant Dining with County-Level COVID-19 Case and Death Growth Rates — United States, March 1–December 31, 2020 | MMWR

They collected data from March 1 to December 31. It’s possible if the high counts into January were included, this small improvement would vanish. Starting and ending points matter a lot when testing effectiveness of strategies.

Restaurant closures and re-opening had little effect:

During the study period, states allowed restaurants to reopen for on-premises dining in 3,076 (97.9%) U.S. counties. Changes in daily COVID-19 case and death growth rates were not statistically significant 1–20 and 21–40 days after restrictions were lifted. Allowing on-premises dining at restaurants was associated with 0.9 (p = 0.02), 1.2 (p<0.01), and 1.1 (p = 0.04) percentage point increases in the case growth rate 41–60, 61–80, and 81–100 days, respectively, after restrictions were lifted

Former CDC Director Robert Redfield said that masks are more effective than vaccines, which have documented 90+% efficacy.

Another study published in the fall of 2020 “found clear evidence that wearing a mask can have a significant impact on the spread of Covid-19 … with a 25 per cent or larger weekly reduction in Covid-19 cases”. That linked press release claimed that indoor mask usage would reduce new cases in Canada by 25 to 40 percent by mid-August (As of early 2021, Ontario is back in total lock down).

As a brain injured idiot, may be I am misinterpreting the CDC study?