What science says about masks
In its response to Covid-19, Australia has been something of a laggard on masks, long insisting they are neither warranted nor necessary. Now, it is an offence in Melbourne and the nearby Mitchell Shire to leave the house not wearing one.
The Victorian government this week became the first in Australia to mandate, with penalties, face coverings in Melbourne and its surrounds as the city confronts a second wave of the deadly virus.
So, what changed?
Victoria’s chief health officer, Brett Sutton, tells The Saturday Paper masks make a “practical difference” in epidemic control, pointing to a growing body of sophisticated modelling that shows they can drastically reduce viral transmission.
“We were following national recommendations on face masks during our first wave, when we had very low levels of transmission in our community,” says Sutton on Victoria’s policy about-face. “Now, with more community transmission, different populations involved and numbers ticking up, I made this recommendation to the government.”
While models make a convincing case for masks, they are only part of the story, particularly when it comes to community use. Much of what is asserted about their efficacy comes from studies in medical settings, mostly looking at the protective effect of surgical or respirator masks for healthcare workers against pathogens such as SARS and influenza.
Few studies have examined the widespread use of masks in the community; fewer still have looked at cloth face coverings, the kind being recommended by authorities the world over. In general, the studies are observational in design, leaving them open to criticisms of bias, and confounding. The question is, how much does this matter?
Professor Julie Leask is an expert in risk communications and vaccine uptake at Sydney University. She says gaps remain in mask studies, and there are uncertainties, but “the truth probably lies somewhere between pragmatics and precaution” in considering whether they are a justifiable and proportionate response.
“When we have an urgent situation like a pandemic and established community transmission, we can’t afford to be methodological purists,” she says.
“Masks should come with reasonable evidence, because they come with some downsides, but if they present a way for people to interact and return to some kind of social and economic life while still providing a form of protection, then they are a reasonable consideration.”
Sutton says masks are a “low-cost, relatively easy action with a small impost”. But Leask adds they are not without risk. They can be worn and disposed of improperly, which increases the risk of contamination and infection. Mandating their use may increase stress on already-pressured medical supply chains. They may become a focal point for community policing and conflict. And the disposable iteration constitutes a truly boggling quantum of landfill.
Perhaps the main concern for public health officials is that the mask directive will result in “risk compensation” – where the perceived benefits of a new intervention prompt the relaxation of more vital protective behaviours.
This is particularly important in the setting of lockdown fatigue, where people may be eager for a justification to be less strict than they were during the first lockdown on staying at home, physical distancing, hand hygiene and getting tested. Premier Daniel Andrews told reporters this week that almost 90 per cent of Victorians were failing to self-isolate when sick, underscoring these concerns.
“It’s an additional protection to be wearing a mask in the community, but it’s only one effect of many, and it will have a lower effect compared to all the basics,” says Professor Peter Collignon, who sits on the national Infection Control Expert Group, one of the key bodies advising the Australian government on its pandemic response.
Brett Sutton insists these concerns are largely theoretical and he is confident Victorians will “step up” and adapt.
Leask says it must be acknowledged no intervention in a complex system is without risk. “In the end, it becomes about combining the best evidence available with the situation we are in,” she says.
Public confusion over masks has stemmed, to some degree, from inconsistencies at the official level. A number of countries were quick to adopt and even mandate face coverings, particularly those with memories of SARS and the 2009 H1N1 pandemic. Others, including Australia, were more reluctant to move.
The United States Centers for Disease Control and Prevention changed its advice back in April, urging Americans to wear cloth masks in public to help drive down infection numbers. It took the World Health Organization another two months to shift its advice, following a systematic review and meta-analysis of all the available literature. In the end, that research came down, with heavy qualifications and a low degree of certainty, in favour of mask use. The analysis, which was published in The Lancet last month, is cited by Sutton as part of his thinking in mandating masks in Melbourne.
Professor Marylouise McLaws, who sits on the WHO expert group responsible for the guidelines, says they worked at unprecedented speed to marshal and scrutinise the evidence, watching in dismay as country after country saw an uptick in cases following the easing of restrictions.
“We were looking for ways we could help that and prevent that from happening, which is why we started focusing on masks in public,” she says.
McLaws describes Victoria’s embrace of the measure as both sensible and timely. She is a self-confessed convert to community mask use, moderating her own scepticism after months of reviewing the evidence, and puts official reticence here down to “cultural disinclination to see the benefit, or rhetoric to protect medical masks”, the latter being a not-insignificant concern early on due to stockpile squeezes associated with the bushfires.
Of the observed epidemiological effect of widespread mask use, McLaws says, “It’s not just theatre, it’s hugely impressive.”
As proof of principle, she points to the Covid-19 curve in countries where face masks in public were normalised at or close to the outset of the pandemic, such as Vietnam, which records four infections per million people. Likewise, Taiwan sees only 19 infections per million, and China only 59 cases per million, despite being the epicentre of the virus early on. Compare this, says McLaws, with countries where the epidemic continues to elude control, including the US – 12,000 cases per million people – and Brazil with 10,000 per million.
Australia is now recording about 500 infections per million people, driven largely by Melbourne’s outbreak, where Collignon estimates one in 1000 Victorians have contracted Covid-19. He says this is a “very high” benchmark that justifies the encouragement of mask use in certain circumstances, such as public transport.
“Masks are useful when you are indoors and you can’t keep physical distancing,” he says. “To mandate them in other areas, I don’t think the science is there for that.”
He notes that most of Melbourne’s transmission in this second outbreak would not have been prevented by face coverings – because these cases have largely arisen from household spread.
Infectious diseases physician Trent Yarwood believes penalising people for not wearing masks is both an ethical and equity concern, saying the “least coercive method is always going to be best”.
“Having the police hand out $200 fines is probably much less useful than the police handing out masks,” says Yarwood, who is based at the University of Queensland.
Sutton stresses that Victoria has a shipment of one million cloth masks due at the end of July and more scheduled for early August. He says that marginalised groups, particularly culturally and linguistically diverse populations and those at risk of severe illness or with access issues, will be prioritised for distribution of these free masks.
Asked why the Andrews government has opted for an enforcement approach, Sutton says: “It’s clear that near-universal mask usage has greater likelihood of suppressing transmission and leading to options for easing restrictions in Victoria.”
This is particularly important for what’s known as “source control” when the state is facing widespread community transmission, he adds, with up to 20 per cent of spread via people who have no obvious symptoms.
Four in five infections, however, will come from someone who is overtly sick but isn’t fully isolating – underscoring the importance of continuing to do the basics: staying at home, especially if sick, getting tested, maintaining physical distance and washing your hands.
“If you are unwell and you wear a surgical mask, then you will cough fewer droplets, but that is significantly less good than you staying at home in your bedroom and not coughing on anyone at all,” says Yarwood. “The best form of source control is non-contact.”
This article was first published in the print edition of The Saturday Paper on Jul 25, 2020 as "Behind the masks".
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