It found that face masks were 79% effective in preventing transmission, if they were used by all household members prior to symptoms occurring..

The remaining study found the use of masks was strongly protective, with a risk reduction of 70% for those that always wore a mask when going out

Both the Australian influenza RCT and the Beijing households observational trial found around 80% efficacy among compliant subjects, and the one SARS household study of sufficient power found 70% efficacy for protecting the wearer.