Coronavirus face masks Q&A: is the advice changing?
Many health authorities, previously discouraged the public from wearing masks to avoid COVID-19. However, emerging evidence has caused the World Health Organization, the US Centers for Disease Control and Prevention (CDC), and the UK government to reconsider whether the public should wear masks. There are of course different types of face masks, and we are mainly considering disposable surgical masks.
Do these face masks work?
Experiments with mock viruses and patients in laboratories suggest surgical masks should help prevent viral illnesses “if used correctly”. Yet, randomised trials done on people in their homes or communities often show little, if any, benefit.
A problem is that many of these studies did not fairly test how protective masks were. In most trials, many people who were supposed to wear the masks didn’t wear them as instructed – and some who were never supposed to wear masks, did wear them. This means the evidence is messy. What these studies mainly show is that it was difficult to get people to use masks as instructed even when participating in a clinical trial.
Other forms of evidence from studies in community settings do suggest that mask-wearers had somewhat fewer respiratory infections than those who didn’t wear masks. However, even taking these many different variables into account, our review found evidence that masks can be most protective for those at higher risk of infection when worn for short periods of time.
Should everyone wear masks?
So far, the official answer in the UK, for example, has been no. Irrespective of the effectiveness of mask use in the community, mass buying by the public has created a shortage for healthcare workers. This puts healthcare workers at risk of getting COVID-19.
But emerging evidence is changing the balance of potential harms and benefits. We know that people are infectious very early after becoming unwell. Other evidence shows wearing masks does reduce the risk of infected people spreading the infection to others.
With this evidence, arguments against everyone wearing masks in public are looking less certain. Countries that previously recommended against wearing face masks in public (including the US) are changing their minds.
But with the current shortage of masks, we have to think carefully about who would benefit most from wearing them. Recent deaths in doctors and nurses remind us of the need to give these people priority.
Based on current evidence, the use of face masks more widely by the public is justified. Wearing masks in public is most beneficial in situations where you can’t properly keep your distance from other people. Wearing masks on crowded public transport is likely to be beneficial – but won’t have any protective effect while walking through deserted streets or in the countryside.
Are there any other problems with wearing masks?
Do cloth masks work?
Cloth masks have large pores and allow moist air circulation – which means cloth masks are less likely to stop virus contaminated droplets from getting through.
What should I do?
Social distancing and frequent hand washing remain the best ways to prevent viruses spreading between you and other people.
If you choose to wear a mask, do not wear it for many hours – four or five hours at most each day. And only wear it when you are in contact with other people, and change it if it becomes damaged or dirty.
Masks can become contaminated from use, not only by COVID-19 but by other bacteria and viruses, so they should be disposed of carefully, making sure to wash your hands afterwards. It’s also important to never share your mask with someone else for this reason.
Paul Hunter is a member of WHO Expert panel on Infection Prevention and Control for COVID-19
Julii Brainard ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son poste universitaire.