Why should we wear a mask?

Face masks are a symbol of the pandemic era – a visual metaphor for the tiny, unseen viral foe that could be lurking around any corner. Some opt for a scarf wrapped around their face, others make do with a t-shirt yanked up over their mouth. The more creative hook colourful homemade varieties around their ears, while a lucky few wear distinctive surgical masks or, rarer still, N95 respirators.

While a few months ago anyone wearing a mask in public would have drawn stares in many countries unused to this behaviour, they are now a reminder of the strange times we live in. And as governments around the world start to ease their lockdowns to allow their citizens out to mingle in the wider world again, growing numbers of people are opting to wear face masks in public.

But there is still debate about whether members of the public should be encouraged to wear face masks at all, and in some places, such as the US, there have been vocal refusals from prominent individuals over wearing face masks in public. Recent polling has suggested around a third of Americans venture out into public without wearing a mask. A YouGov poll conducted in March suggests that in Spain, Italy and China over 80% of people asked say they wear face coverings. The UK has one of the lowest adoption rates, with just 36% of people saying they wear a mask, but the government there has now announced it will make wearing face masks compulsory in shops from 24 July 2020.

“A key point is that the countries that flattened the curve used masks in public,” says Chris Kenyon, head of the sexually transmitted diseases unit at The Institute of Tropical Medicine in Antwerp, who has examined whether face masks may have played a role in limiting the spread of Covid-19 in certain countries. “These were mostly Asian countries. For some reason, until very recently European experts – Czechia (Czech Republic) excluded – were unable to learn from what worked in Asia.”

To understand why face masks might work, it is important to look at how the virus that causes Covid-19 spreads in the first place.

Once it has infected someone, the Sars-CoV-2 virus responsible for the disease hijacks their cells to replicate itself. As it multiplies, these new virus particles then burst out of the cells and become suspended in the bodily fluids in our lungs, mouth and nose. When an infected person coughs, they can send showers of tiny droplets – known as aerosols – filled with the virus into the air.

A single cough can produce up to 3,000 droplets. There are fears the virus can also be spread simply through speaking. One recent study showed that we spray thousands of droplets invisible to the naked eye into the air just by uttering the words “stay healthy”.

Once out of our mouths, many of the larger droplets will quickly settle onto nearby surfaces while smaller ones remain suspended in the air for hours, where they can be breathed in. While the behaviour of the virus-filled droplets in rooms with air conditioning and outside environments are less well understood, they are thought to settle on surfaces more quickly in disturbed air. There are also some reports that the coronavirus can spread through ventilation systems in buildings.

The Sars-CoV-2 virus has been found to survive in these aerosol droplets for at least three hours, according to one study by virologist Neeltje van Doremalen and her colleagues at the US National Institute of Allergy and Infectious Diseases, Hamilton, Montana. But a more recent, but as yet unpublished study, has found that the Sars-CoV-2 virus is still infectious for more than 16 hours after being suspended in aerosol droplets. It found the virus was “remarkably resilient in aerosol form” compared to other similar coronaviruses they studied.

Together, they suggest that in the right conditions, the virus can linger in the air for several hours and still infect people if breathed in. And in indoor environments, they seem to be particularly prone to spreading through the air.

An unpublished analysis of 318 outbreaks of Covid-19 in China showed that it was most commonly transmitted in indoor environments, particularly in people’s homes, but also on public transport, in restaurants, cinemas and shops. They found just one example where the virus appeared to have been transmitted while people were outside.

“One of the proposals for lifting lockdowns is that we use mass testing along with contact tracing and quarantine, to get ahead of infections in the community,” says Cowling. “If you are identified as an infected person, the health department can trace your family members, your social contacts and your occupational contacts, but it is very difficult to trace who you were sitting next to on the bus or train.

“If we can limit transmission in these kinds of locations, it could really be a big help.”

One of the reasons widespread, public face mask wearing is so important with Covid-19 has to do with the prevalence of asymptomatic carriers who can still spread the virus to others. It is estimated that anywhere from 6% to almost 18% of those infected can carry the virus without developing symptoms. Add to this an incubation period of around five days, but up to 14 days in some cases, before symptoms develop and even those who do go on to show signs of being contagious can spread the virus to a lot of people before they start to fall ill.

“This makes it particularly difficult to suppress transmission in the community,” says Cowling. “But if everybody is wearing face masks, that would mean infected and asymptomatic people are also wearing masks. That could help to reduce the amount of virus which gets into the environment and potentially causes infections.”

“We have little to lose from the widespread adoption of facemasks, but the gains could be significant,” says Renata Retkute, an epidemiologist at the University of Cambridge, who was one of those involved in the study.

Venki Ramakrishnan, president of the Royal Society, one of the UK’s most presitigious scientific bodies, has also added his voice to the debate, urging everyone to wear face coverings when in enclosed pubic spaces. He believes we should now be treating face masks as just “another item of clothing” we would wear when we venture out of our homes.

“If all of us wear one, we protect each other and thereby ourselves, reducing transmission,” he says. “We lower the chances of future surges and lockdowns which are economically and psychologically disruptive, and we increase the chance of eliminating the virus.”

In countries where masks are in short supply, some researchers have suggested that prioritising them for the elderly could also be effective.

While face masks might bring a little discomfort, and make it harder to spot the facial expressions of those we are talking to, those things are a small price to pay for keeping the people around us safe and well.

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