Dr Rochelle Walensky from CDC is claiming in advertisements, without evidence, that wearing a mask could reduce the risk of infection by 80%. However, a Cochrane study by Jefferson et al. and a report of the European Center of Disease Control concluded there is no high-quality evidence in favor of facemasks. No association was observed between mask mandates or use and reduced Covid-19 spread in US states. Up to now there are no results available of randomized clinical trials that could demonstrate beyond any doubt that wearing masks prevent people from viral infection and could slow the spread of the virus.

Randomized controlled trials during this pandemic on the effects of wearing medical masks in Denmark by the general population could not alter the conclusions of previous trials with (medical) masks on the spread of influenza virus in a hospital setting or in non healthcare settings there is no substantial effect.