We don’t have a study that shows washing our hands is an effective way to avoid some of the infection from this virus either, but based on how we know viruses work it’s pretty certain that hand washing will help. I don’t understand the fixation on having scientific studies on everything (masks, indoor dining, etc). We have a lot of knowledge on how the virus spreads so we know certain things will be more or less risky based solely on that. Indoor dining is more risky than outdoor dining which is more risky than takeout which is more risky than cooking at home.