Effectiveness of Face Mask or Respirator Use in Indoor Public Settings for Prevention of SARS-CoV-2 Infection — California, February–December 2021 | MMWR

No big Surprise. Wearing a good #ffp2 mask indoors is very good at preventing being tested positive
#covid19 #masks #ffp2

https://www.cdc.gov/mmwr/volumes/71/wr/mm7106e1.htm