Louis M. Katz MD and Cheryl True MD
Should masks be used in community settings (not health care) to prevent COVID-19? The question is important as we come into fall and winter when cold weather will drive people indoors and into crowded settings. Early advice not to use masks in public were driven by our lack of understanding of how often the virus was transmitted from people without symptoms and the need to save masks for frontline healthcare workers when supplies were short. People with no symptoms cause a large part of transmission and shortages are largely gone.
The best proof that masks work, controlled experiments, is not available, but the other evidence is convincing. Animal experiments and observational studies show that masking of both infected people and contacts greatly reduces transmission of SARS-CoV-2. This makes sense: they block the virus from getting out of an infected person and from getting into the airway of a contact. They may also reduce the severity of COVID-19 even when full protection fails (probably by reducing the amount of virus that establishes an infection). (Source)
These can be well controlled and are very convincing.
Hamsters have been infected with SARS-CoV-2 and housed next to uninfected animals with their cages separated by either screens or mask material. If separated by mask material, they have less than half as many infections and those that are infected become less ill. (Source)
These provide useful data but can be confusing when two or more interventions are used at the same time.
Two large trials randomized experiments in humans should be available in the near future.
One in Denmark has been completed in which 6000 people were randomized to a request to use masks in workplace or not. The study is completed but no results are available.
A study is in progress in Guinea-Bissau with 40,000 people in households randomized to receiving masks or not. All will receive advice on how to protect themselves from COVID-19. The study is to be fully enrolled during November, with the participants followed for COVID infections for several months.
Masks work to prevent COVID-19. The White House Coronavirus Task Force recommended a mask mandate in Iowa because of uncontrolled spread in the state. Masks are safe, simple, and cheap. (Source) Absent mandates, businesses are in a perfect position to require masks on their premises and individuals to model mask wearing as an expected pro-social behavior. Masks combined with scrupulous social distancing, hand hygiene and other recommended prevention measures are a critical part of COVID-19 prevention strategies.
Louis M. Katz MD and Cheryl True MD are the medical directors of the Scott and Rock Island Co. Health Departments, respectively. Their opinions to not necessarily reflect the official positions of either department.