While more than 130 countries now have mandatory mask policies to help curb the transmission of SARS-CoV-2, the virus that causes Covid-19, their decisions to do so were initially based on ‘fledgling science’ and a ‘precautionary principle’ approach: better safe than sorry. Now, wearing face coverings to help prevent Covid-19 transmission is backed by a growing body of evidence adding scientific heft to this cheap, effective method – especially if the virus is proven to be airborne.
The ongoing need to prevent Covid-19 infection on a massive scale involves a balance of efforts between government and citizens. While the government is responsible for (and, in South Africa’s case, not doing brilliantly at) the test-trace-isolate side of the equation, each of us, individually, is responsible for wearing a mask, maintaining physical distancing at all times, and frequently washing or sanitising our hands. These are measures that, consistently and correctly practised, work.
Like everything with this coronavirus, research into the details of masks’ effectiveness is still evolving and yet to be universally endorsed. But it is evolving fast. The most alarming idea gaining traction in the scientific community – one that we all fear but haven’t had confirmed – is that the coronavirus (SARS-CoV-2) may be airborne.
Airborne transmission theory means everyone is more at risk
Until now, the belief has been that the virus is spread via “large” droplets (the width of a human hair) that are expelled when a person coughs or sneezes. Droplets are heavy enough to quickly drop on to surfaces or the floor after expulsion – and this has been the logic behind the universal one-to-two-metre physical distancing idea. As we know by now, the droplets are directly infectious if they touch our eyes, noses or mouth, including if they are picked up from contaminated surfaces such as door handles.
But aerosols, or “microdroplets” – particles that are much smaller than “droplets” but that also contain virus – are much lighter, and have been shown to remain in the air, floating and recirculating for hours, and possibly building up over time in enclosed or poorly ventilated spaces. If this is true, still greater vigilance – by each and all of us – will be needed to prevent transmission of the virus.
The World Health Organisation (WHO) has not yet fully backed the airborne-transmission idea. It only officially changed its mask policy on 5 June 2020, to include members of the public at risk of “droplet” transmission “within households and among contacts of cases”, or while attending mass gatherings. But the WHO is renowned as a cautious, totally evidence-based entity that can be slow to decide anything while it waits for what it considers to be incontrovertible evidence from its own studies. The WHO’s own investigation into aerosol transmission, in collaboration with scientists around the world, is under way, examining exactly how or if virus-bearing “microdroplets” could be circulating, and how infectious they are.
During the ongoing study, in July 2020, in a move that startled many, some of the same scientists collaborating on this with the WHO temporarily broke ranks and independently published an open letter appealing to the medical community and to national and global bodies “to recognise the potential for airborne spread of Covid-19”. The inference being that the ongoing investigation has merit, but the WHO is not acting fast enough.
“There is significant potential,” the scientists’ letter reads, “for inhalation exposure of viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several metres, or room scale).” The letter, published in the Oxford academic journal Clinical Infectious Diseases, was signed by 239 scientists.
The WHO’s response has been to recognise that the virus spreads in “closed spaces” but that it needs to see the study’s results before creating guidance for governments on new interventions to contain Covid-19.
Whether you swear by the WHO’s guidance or not, whether you have been susceptible to controversy around mask-wearing or not, it makes sense for all of us to wear them, properly and consistently.
Yet it is clear to anyone who sets foot outside their home that not all South Africans outside of workplaces where the policy is enforced are complying, to put it mildly. From people living on the street to minibus taxi hailers shouting into people’s faces, to privileged joggers and cyclists who consider themselves above it, the reasons for this are many and varied.
They range from the inability to obtain or afford a mask to lack of accessible-enough information about why wearing one is necessary, to garden-variety scepticism, machismo, or in-your-face, “gatvol” contrarianism, overlaid (in some cases) by a properly, self-righteously South African sense of entitlement to do whatever the hell you want.
But the case for masks is increasingly compelling, even if the discussion in the public domain in South Africa around these ideas has not been resoundingly clear. In addition to the strong likelihood of airborne transmission:
Masks work most effectively as ‘source control’.
The main idea conveyed in public health messaging around the world at the beginning of the Covid-19 outbreak was that mask-wearing would help prevent you from getting infected, in case someone coughed or sneezed in your face. The emphasis has shifted with the likelihood of airborne transmission: masks have been shown to be at least as effective (if worn correctly) at preventing virus-laden microdroplets from escaping outwards during talking and breathing, as from coming in. Indoors, the effect is cumulative – if everyone wears a mask, the total viral load in the air in the room drops (see the next point).
A study in the influential journal Nature Medicine examined 111 people infected with respiratory illnesses (influenza, rhinovirus, and a milder coronavirus) and had them exhale into a funnel, with and without simple masks. The lead author of the study, Ben Cowling from the University of Hong Kong’s School of Public Health, said that looking at all the results, “we found that masks were able to stop most virus-laden respiratory droplets and some of the virus-laden aerosols”.
The greater the number of people who wear masks, the better they work.
Experts agree that masks work best when compliance is high. A review of the evidence by 19 internationally renowned scientists shows that the more people who wear a mask in public, the lower the transmissibility of the virus. This is especially true in places – like South Africa – where clearly the test-trace-isolate approach to managing the Covid-19 epidemic is not functioning very well, especially with slow testing turnaround times, making all contact tracing and isolation attempts almost meaningless if they only happen a week after a symptomatic person is tested.
Taken together, the high proportion of asymptomatic carriers of Covid-19, the often unavoidably crowded conditions in which people live and have to travel every day, and the obstacles to effective testing all make the case for mask-wearing – and enforcement – in South Africa an urgent priority. (In the United States, where widespread lack of mask-wearing has been associated with virulent flare-ups in new coronavirus cases, the Washington Post says mask-wearing mandates must be backed by fines and even arrest. “There is no time to waste on half-measures,” the opinion piece states. “Success hinges on clear and consistent enforcement that everyone understands.”)
Asymptomatic and pre-symptomatic transmission of Covid-19 is possible.
Researchers have estimated that the proportion of Covid-19 cases that are asymptomatic – people who are infected but never develop symptoms – is as high as 40%. This means a large number of us are infected and don’t know it. And infection from people who don’t have – or don’t yet have – symptoms may be responsible for between one third and half of all infections.
Even for those who do develop symptoms, studies have shown that SARS-CoV2 “viral load” (the amount of virus in an infected person’s body) peaks in the days before symptoms begin, and that talking is enough to emit droplets or microdroplets containing virus particles. Either way, we may all be transmitting the virus wherever we go, simply by breathing and talking.
The best mask is the one you are going to wear.
The essence of the idea behind mask-wearing is “risk reduction” rather than risk elimination. Whatever kind of mask you wear, it is going to be better than none. And in order for you to wear it, it must be comfortable (enough) to wear for prolonged periods.
The science on which types of masks – apart from the surgical-grade N95 respirators for medical staff and other surgical-grade masks – offer the most protection is not yet clear. But among the US Centers for Disease Control and Prevention, the WHO, and the UK’s Royal Society there is consensus that cloth masks offer significant protection from droplets coming towards you, and most importantly substantially prevent virus-laded microdroplets from being spread by the wearer.
An American study evaluating the effectiveness of 13 different kinds of material used in 400 homemade masks looked at which types of masks and mask material were best at filtering out particles of 0.3-1 microns in diameter (one micron is 1/1000th of a millimetre, microdroplets are between 0.7 and 10 microns, and the SARS-CoV-2 virus itself is 0.1 micron).
The study showed filtration effectiveness of 97% for N95 masks, 79% for the best homemade cloth masks, and 62%-65% for surgical masks.
The best-performing designs, the study said, were masks made of two layers of high-quality, heavyweight cotton (with a thread count of 180 or more), especially those cotton fabrics that were tightly woven and with thicker threads.
Ten mask rules to live by:
- A mask only works if it covers your nose and mouth – wear one with a close fit over the bridge of your nose.
- A mask does not work if it is even a few millimetres off your nostrils or mouth area – let alone on your chin (the virus doesn’t give you immunity credits for pretending to wear one).
- Wear a double-, triple- or quadrupled fabric mask if possible (adding a paper towel to the inside of your mask could filter even better).
- Wash and dry your worn mask after every outing, so have at least two (cloth) masks, if you can.
- If using disposable surgical masks, throw them away after every outing.
- Mask or no mask, being inside is much riskier than being outside. (You don’t need to wear a mask at home unless someone is sick, in which case you should wear it all the time.)
- Air-conditioning systems may recirculate virus particles in air-conditioned but poorly ventilated indoor spaces (a preprint, i.e. not yet peer-reviewed, study in Japan estimated that the risk of indoor transmission is 20 times higher than outdoors).
- Give unmasked runners and cyclists, especially those in front of you, a wide berth – some research shows that respiratory particles from fast-moving people are present in their narrow slipstream for several metres (or more, the faster they are going).
- If you are still one of the sporty unmasked, unhappy with masks’ poor fit, there are now many types of high-tech sports masks designed for runners and cyclists that are game-changers.
- Adopt – and spread – the “ubuntu” approach to mask-wearing: “A protected person is a protected person through other protected people,” or “I am protected because you are protected.”
This year’s World Mask Week runs from 7 to 14 August 2020.
Having a “world mask week” is a bit like having an annual “women’s day” – there is never a time when the subject is not relevant. Nonetheless, World Mask Week is designed to raise awareness of #MaskingForAFriend, a campaign by the Pandemic Action Network to raise awareness about the benefits of cloth mask-wearing among the general public. Siya and Rachel Kolisi are launching the campaign in South Africa. DM/MC
Adèle Sulcas writes about global health, food systems, and the wine industry. She has worked at the Global Fund to Fight AIDS, TB and Malaria and the World Health Organisation, and is an adviser to Internews’ Pandemic Media Mentors.