Masks and Covid-19: What the recent (fledgling) science says

Despite repeated advice from the World Health Organisation that wearing a face mask to protect against Covid-19 is necessary only for health workers who are in direct and prolonged contact with people who are infected with the virus, humans everywhere are clamouring for just about any version of a face mask available. Flimsy disposable paper masks, construction workers’ masks, and, more recently, cloth masks or scarves or bandannas, are filling the gap, in the absence of commercially available surgical N95 masks, which the New York Times recently described as “perhaps the most sought after product on the planet”.

And with good reason – they are in radically short supply the world over, which is possibly why the World Health Organisation and several governments have policies discouraging the use of face masks for all but frontline health workers. Encouraging them for the general public would place additional strain on an already unbearably stretched global market for personal protective equipment. 

But in many countries, this policy has shifted in the past few days, including in South Africa. First, national policy discouraged the use of face masks, as Daily Maverick has reported. The Department of Health stated:

“Personal protective equipment (PPE) is a scarce commodity and should be used appropriately and by the appropriate people. If you are not ill and not in close contact with someone who has coronavirus, you do not need to wear a mask or gloves.” The Western Cape Department of Health released its own statement reiterating that “for the general public no PPE [personal protective equipment] is needed”.

Then, on 1 April, Health Minister Zweli Mkhize recommended the use of masks as “one of the best ways of preventing the spread of infection” and on the same day Transport Minister Fikile Mbalula mandated that all minibus taxi passengers must wear N95 surgical masks (with taxi capacity at a maximum of 70%). How this is being practically enabled, or enforced, is unclear. The Western Cape Health Department also changed its stance on 2 April, saying, “as the epidemic unfolds, the wider use of masks are indicated even for people who are not ill, especially if they move around in the public.”

The World Health Organisation, which is leading the global response to Covid-19, has not altered its very clear guidance for the public, advising against wearing masks unless you are taking care of a Covid-19-infected person, or are yourself coughing and sneezing. (They also advise on how to dispose properly of masks, critically important as repeated use of disposable masks, perhaps by different people, could aggravate the possibility of infection.)

But countries with recent and hard-earned experience with Covid-19 say otherwise – China, South Korea, Hong Kong and Singapore are among those where absolutely everyone wears masks (though it’s not official policy) arguably with some positive effect on changing the trajectory of their epidemics, which are more under control than those in the West.

Mixed messages aside, our anxiety, plus our survival instinct, is compelling most of us to cover our faces – and some recent science is backing up this self-protective urge.

On 2 March, the authoritative medical publication The Lancet published a letter from a group of Chinese scientists, “Mass masking in the Covid-19 epidemic: people need guidance”. The letter, written while China’s epidemic was still surging, urged policymakers to reconsider the role of masking, and to encourage their widespread use.

Two weeks later, The Lancet published a paper that looked at the “viral load” of patients with Covid-19 – the level of virus present in individual infected patients. The study found a correlation between the viral load of patients with Covid-19 and the severity of the disease:

“The mean viral load of severe cases was around 60 times higher than that of mild cases, suggesting that higher viral loads might be associated with severe clinical outcomes,” the paper said. Meaning simply that it is possible that the more virus a person is carrying, the more serious the symptoms they experience. (And potentially the more virus particles they might exhale.)

Then, on 3 April, Nature Medicine published the results of a study on “respiratory virus shedding in exhaled breath”, which said very plainly that the study “demonstrated the efficacy of surgical masks to reduce coronavirus detection and viral copies in large respiratory droplets and in aerosols”. This, the authors said, had important implications for the control of Covid-19, “suggesting that surgical face masks could be used by ill people to reduce onward transmission”.

The study analysed the exhaled breath of 111 subjects, 90% of whom were infected with Sars-CoV-2, and the other 10% with seasonal flu virus and/or a rhinovirus. Half of the subjects exhaled through a surgical face mask, half of them exhaled without a face mask. The authors “detected coronavirus in respiratory droplets and aerosols in 30% and 40% of the samples collected without face masks, respectively, but did not detect any virus in respiratory droplets or aerosols collected from participants wearing face masks” (this writer’s italics.)

Given the universal shortage of medical-grade masks, the WHO’s and other countries’ advice is, for now, pragmatic, and well-intentioned – to save the meagre supplies of surgical masks for frontline health workers.

It does seem logical, though, that a physical barrier, even if it only blocks the biggest of droplets containing virus particles, is better than no barrier at all. Robert Redfield, Director of the US Centers for Disease Control, on 4 April was unequivocal about the utility of a simple cloth mask in helping to prevent the spread of the virus, and went on to recommend that all Americans use one.

“There is scientific data to show that when you aerosolised virus through a cloth barrier, you have a reduction in the amount of virus that gets through the other side,” he said, suggesting “kind of a homemade, make-it-yourself barrier, whether it’s a bandanna or a scarf”. This was the same day that President Donald Trump gave his mixed-message recommendation that all Americans wear cloth masks (but also stating that he wasn’t going to).

The US’s guidance is intended less to protect the wearer of the mask than to protect everyone else, by preventing people who may not know they are infected from spreading the virus (this coronavirus is contagious up to two days before the onset of any symptoms in an infected person – and sometimes there are none).

Taking The Lancet’s viral-load paper’s implications a step further, the results could mean that masks play an enormous role in reducing the amount of virus an infected person’s exhalation puts out into their immediate environment – potentially a significant prevention mechanism, particularly in crowded settings. Multiply the collective viral load of tens or hundreds of people in a public space and logic dictates that it’s going to be higher without masks than with them.

Another group of Chinese researchers writing in The Lancet on 20 March said “as evidence suggests Covid-19 could be transmitted before symptom onset, community transmission might be reduced if everyone, including people who have been infected but are asymptomatic and contagious, wear face masks”.

For South Africa, “community transmission” is critical – this is the type of epidemic we have, and given the crowded conditions in which millions of people in South Africa live, crowded spaces are where most new infections are likely to happen.

And there may be additional, less quantifiable benefits to broad masking policies – as the New England Journal of Medicine points out – “beyond their technical contribution to reducing pathogen transmission”. There is a symbolism that is at once about the wearer acknowledging and respecting their role in community prevention and taking recourse in some sense of control over their health.

Whether their value is actually in their ability to prevent infection or largely symbolic, masks play an important role. Put (a cloth) one on (and then take it off properly, and wash it). DM

World Health Organisation’s ‘When and how to use face masks’.

Western Cape Department of Health’s detailed guidance for the public on the use of cloth masks.

If you really have time on your hands, you may want to attempt following the New York Times’s tutorial on how to make a face mask.