Face coverings add an extra layer to our armour in the fight against Covid-19, but some are much better than others, experts say. By Andrea Graves
Doctors tending to black-plague patients in 17th-century Europe felt vulnerable. They believed the disease was spread by bad air known as "miasma", making every breath risky. So they wore beaks containing dried herbs, spices and flowers thought to purify air inhaled through holes at the beak's tip.
For centuries, miasma was also blamed when people in warm climates were sickened or died after breathing swamp air. The actual culprit, of course, was the malaria (mal-air) parasite transmitted by mosquitoes.
Plague was eventually revealed to be due to a bacterium spread by flea bites, contaminated tissue or fluid, and sneezes or coughs from infected lungs.
Unlike miasma believers of the past, we know that germs exist. We need to understand their strategies for spreading between victims if we are to devise countermeasures to prevent ourselves become infected.
The virus that causes Covid-19 spreads chiefly via a strategy that's virtually airborne pestilence: minuscule virus-laden particles borne on exhaled breath.
This summer, the virus will literally hang in pockets of air from Cape Reinga to Rakiura. What is the best way to protect ourselves and others?
Face masks work to intercept these tiny particles, which are also known as aerosols.
"Until now, masks haven't felt like a matter of life and death as they did in many countries that had the virus before they had vaccination," says Professor Michael Baker of the Ministry of Health's Covid-19 technical advisory group and the University of Otago, Wellington.
"We now have vaccinations, which are the No 1 intervention, but not the only one. Vaccination does well at preventing severe Covid-19 infection and death, but it is not fully protective against infection. Masking is an extra layer of armour."
And although the vaccine's protection against severe illness remains high for at least six months, it wanes against infection. According to a Ministry of Health spokesperson, recent real-world findings show that four months after a second Pfizer vaccination, protection against infection declines from over 90 per cent to about 53 per cent.
So, even the double-vaccinated should wear masks, says Baker. He advocates for universal masking in most indoor environments outside the home for the foreseeable future.
He says about 60 per cent of people who spread the virus have no symptoms, and the chance of spreading is highest before people notice symptoms, anyway.
There's solid evidence that masks help. Results from real-life studies among people such as hairdressers and sailors, and lab experiments in which ill people speak or cough, consistently show that masks reduce the number of airborne infected particles and coronavirus transmission.
A recent analysis of 35 studies showed that, on average, mask-wearing halves incidence of infection. The World Health Organisation and the US and European Centres for Disease Control recommend communities wear masks.
In New Zealand, masks will be required or recommended under the Covid-19 Protection Framework, especially at red or orange levels.
The discovery that the coronavirus is spread mainly via aerosol transmission changed everything, says Dr Felicia Low, a research fellow at the University of Auckland's Koi Tū: The Centre for Informed Futures.
She led a recent Koi Tū evidence review on masks. "When Covid-19 first emerged, we thought it followed the same route as the common cold or influenza, which spread via droplets. But although it does spread via droplets, we know now that the main way is aerosols, which are also particles of fluid that emerge from the mouth and nose but much, much smaller ones. They spread incredibly easily – you don't even have to open your mouth!"
We exhale aerosol particles when we sing, whisper, talk, laugh, and puff during exertion. Coughs and sneezes blast them out, but we expel them even during at-rest breathing. Because the virus coats the throats and noses of people with Covid-19, the particles they exhale become loaded with virus.
Like cigarette smoke, these exhaled particles can travel for many metres, can float for hours and are easily inhaled into others' lungs. Inhaling invisible, odourless, virus-ridden particles is the main source of Covid-19 infection.
"Physical distancing can only protect you against the larger droplets, because aerosols can travel much further than two metres," says Low. "Wearing a mask to trap the aerosols is much more important protection."
The upside of aerosols is that breeze whisks them away. "It's usually unnecessary to wear masks outside," says Baker. "If you're in a well-ventilated outdoor area, the chances of getting the virus are negligible. The only exception might be if a group of people congregate closely in a quiet corner."
Where activities can't be taken outdoors, masks should be worn, he says, and a breeze provided by opening windows or otherwise ventilating rooms so air flows away from people.
Darth Vader helmets
During early 2020, social media entertained with people's outlandish mask efforts, from strapped-on meat trays and kitchen sponges to sanitary pads and Darth Vader helmets.
There's still space for chuckles, but when choosing a mask, the priorities are effectiveness and comfort. "The aim is twofold: to protect the wearer from inhaling aerosols from the outside and to catch droplets and aerosols expelled by the wearer," says Low.
Hospital staff wear N95 masks because they provide the best protection, but only if they're properly fit-tested. "If you haven't been trained how to wear them, they won't provide you with the protection you think they do, and they're expensive," says Low.
Baker agrees. "This is distinct from wearing PPE [personal protective equipment]. That should be reserved for occupational settings like hospitals and MIQ where staff are regularly exposed to infected people, and for highly vulnerable groups such as those who are immune compromised. Universal masking as a public-health measure doesn't have to be quite as effective as PPE; it only has to significantly reduce infection risk to make it worthwhile."
Most disposable masks are the blue-and-white surgical masks. Low says these are designed to protect from splashes and droplet infections, but aerosols can sneak in and out around gaps. "If you don't do any tweaks to get rid of air gaps, even surgical masks are only 50-75 per cent effective at filtering aerosols. But with tweaks to tighten the fit, they can be up to 90 per cent effective."
She recommends reusable cloth masks where possible to minimise environmental impacts and save money. "We're going to be wearing them for quite some time, and they'll soon pay themselves off." Cloth masks, too, must fit snugly around facial contours.
Dr Richard Everts, infectious disease specialist and microbiologist at Nelson Bays Primary Health, is dubious about cloth masks. "The diversity of fabric masks is huge. I've seen people wearing fabric masks that fall off their face as they talk. Many are made by well-meaning people who follow patterns and advice, but are these based on any good research?"
Everts also works at the Nelson Marlborough District Health Board, which he says has banned cloth masks for healthcare workers because it lacks the ability to test them and can't guarantee they are effective. Some airlines, too, have banned them due to their variable effectiveness, and the French Government requires that cloth masks meet certain specifications.
But the Koi Tū report said that cloth masks can work well. The fabric type and number of layers matter: some fabrics perform terribly, and three layers are generally required to successfully intercept aerosols.
Effective fabric combinations shown to filter 70-90 per cent of droplet and aerosol particles include tightly woven, high-thread-count cotton with two inner layers of natural silk or polyester chiffon or one of flannel. One layer of fabric helps, but not much.
"Wrapping a scarf around the face isn't going to cut it," says Low. Bandannas are off the list, and masks with exhaust valves protect wearers but do nothing for people nearby.
An inner layer of polypropylene – the stuff that reusable bags sold by supermarkets is made of – should also filter effectively, says aerosol chemist Joel Rindelaub from the University of Auckland, who co-authored the Koi Tū report.
Like silk, chiffon and flannel, polypropylene can hold an electrostatic charge that droplets and aerosols cling to as they pass. But does this charge survive washing? "Maybe not," says Rindelaub, "although rubbing the fabric while wearing rubber gloves might help replenish it."
Engineers at Northeastern University in the United States tested many cloth masks and found that cone-shaped ones with flexible nose-bridge wires fitted best and filtered out 80-90 per cent of droplet and aerosol particles. Cone-shaped masks have seams that curve the fabric outwards, like a distorted bra cup.
The engineers confirmed that the fit of surgical masks is usually gappy, but their material filters more effectively than cloth. Surgical-style cloth masks performed poorly.
Baker wants a national masking strategy, including guidelines on what kinds of masks are needed in specific settings and a performance standard that all masks should reach. Not everyone can afford a decent mask, he says, and some governments overseas have provided reusable masks to their entire population.
He worries that some of our traffic-light levels may be too lax on mask-wearing by relying on "encouragement".
He wants masks prioritised in high-risk indoor environments and during activities such as singing and dancing and loud conversations in noisy settings where people inhale and exhale aerosols heavily.
But with summer coming, who wants a stuffy face and stale lungs? Masks don't actually restrict oxygen, says Baker, citing lab studies on people exercising vigorously with no decline in blood or muscle oxygen levels or exercise performance.
It's not culturally normal to wear masks here, says Low, but we'll have to get used to them. "We can learn a lot from other cultures who have long worn masks as a matter of routine. In parts of Asia, they have experienced Sars and seen how devastating it is.
"They have the same level of discomfort as us in heat, but they have accepted it as a way to keep themselves safe."