The Centers for Disease Control and Prevention (CDC) and others have changed recommendations about masks because the scientific consensus has changed as more has become known about the novel coronavirus. For example, with most infectious diseases, the sicker you are and the longer you’ve been ill, the more infectious you are. This isn’t how covid-19 spreads. Studies have found that the amount of virus in the mouth and nose of an infected person is highest in the days before and soon after they feel sick, then decreases steadily. With covid-19’s close cousin, severe acute respiratory syndrome, it’s the opposite — viral load increases steadily over the first seven to 10 days. Studies then emerged showing that a high proportion of infected people didn’t feel sick but had large quantities of virus in their mouth and nose and could spread the virus. These findings prompted the CDC to recommend masks.
Masks are highly effective at protecting others and at least somewhat effective at protecting ourselves. One analysis from Germany suggested a 47 percent reduction in virus spread just from mask-wearing, and another study suggested that three quarters of a country’s increase could be prevented by mask use. Had the United States adopted mask use earlier, this might have translated into a hundred thousand fewer deaths, millions fewer lost jobs and businesses and a faster economic recovery.
Which masks are best? There are few good studies on this, surprisingly, and findings are inconsistent, but it’s clear that just about any face covering is better than none. Today our epidemic prevention team at Resolve to Save Lives, an initiative of the global public health organization Vital Strategies, released a brief reviewing the science. Surgical masks are highly effective, and for the highest-risk situations, a medical N95 mask without an exhaust valve is safest. In other countries, governments increased production of surgical (and N95) masks, guaranteed their availability and cost, and distributed them as necessary. The United States could have done this through robust use of the Defense Production Act and other means, and still should. Shortages of N95 and surgical masks may have also led to less effective federal leadership on appropriate mask use.
The profusion of homemade face masks, although they may encourage use and engage volunteers and communities in production, obscures important differences in effectiveness. If an N95 or surgical mask isn’t being used, a tightfitting mask with three layers consisting of cotton or cotton-synthetic material is next best.
When should masks be used? Masks don’t need to be worn in those few places where covid-19 has been confirmed not to be spreading, or generally outdoors except when people are packed close together, unable to stay six feet apart, particularly for long periods of time. Yes, I’d feel safer if the person walking past me on the sidewalk wore a mask, but the risk from a fleeting, passing outdoor contact — as long as that person isn’t sneezing, coughing, shouting or singing close to me — is extremely low. But in any public indoor area where others are present and there is any community spread of covid-19, masks are essential to reduce risk.
Although mask-wearing has increased in the United States, it remains lower in men than women, lower in the South than the North, and lower than in countries that have used masks most extensively to limit covid-19. How can we increase mask use?
First, make masks readily available and comfortable, and encourage their use as a social norm. Employers must provide — free — surgical or N95 masks to vulnerable and essential workers, including meatpackers and grocery and pharmacy staff. States including Michigan and private companies have increased supply and normalized masking up. Others should follow suit.
Second, implement mask mandates that are easy to understand, and require businesses to make a good-faith effort to enforce mandates, including, certainly, for all employees.
Third, monitor mask use, as Philadelphia does, and adjust communications campaigns to increase correct mask-wearing. What is measured can be managed. Rigorously designed and evaluated communications campaigns and community engagement can further increase correct mask use.
Mask use won’t end the pandemic, of course. Masks must be combined with comprehensive action, including closure of indoor spaces when appropriate, protecting health-care workers and health-care facilities, physical distancing, hand-washing, ventilation, strategic testing, rapid isolation, complete contact tracing and supportive quarantine. Unlike most other measures, however, masks don’t cost much and don’t interrupt our usual activities: They are among the cheapest, simplest and most effective ways to fight the virus and get the economy running again.
Masks need not separate us from other people. Properly designed and worn, they simply separate us from the virus.