After the United States recommended citizens make their own cloth face masks, experts weigh in on their effectiveness
Research shows surgical masks work, but even the gold standard N95 respirators should not be used as a substitute for social distancing, scientists warn
With the World Health Organisation as well as countries led by the United States, Singapore and Canada now recommending the use of masks or makeshift facial coverings to contain the spread of coronavirus, the rush to secure supplies has intensified.
In the US, where there is a shortage of personal protective equipment (PPE), authorities have encouraged people to make their own facial coverings to ensure that surgical masks and higher end respirators are reserved for frontline medical staff.
While there has been little clinical research about how effective makeshift masks are, experts said that the recommendation by the Centres for Disease Control and Prevention (CDC) represented a “contingency plan, as the US is struggling with their dire lack” of
“It looks like their strategic stockpile is less than what we have expected, so I understand why they gave this recommendation,” said Chane-Yu Lai, associate professor at Chung Shan Medical University in Taichung, Taiwan.
There is a spectrum of evidence about the effectiveness of facial coverings for protecting both the wearer and wider society, but medical experts agree that they should not be a replacement for containment efforts, such as rigorous hand washing or social distancing. There is also consensus, however, that in times of emergency, some sort of face covering should be worn if you leave your home.
“The concept is that something is better than nothing,” said Benjamin Cowling, head of epidemiology at Hong Kong University (HKU) and one of the authors of a groundbreaking recent study published in the journal
, which concluded that “surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals”.
meanwhile, initially told residents that masks were only needed for those who were sick and on their way to see a doctor. After an about-turn on mask guidance at the end of last week, the government is issuing reusable cloth masks to every household to conserve surgical masks for medical staff.
The reusable masks, however, only provide “basic protection”, said the government, and are meant for people who need to go out for essential purposes such as buying groceries.
In 2015, Abrar Ahmad Chughtai, a lecturer in international health at the University of New South Wales in Sydney, helped conduct the world’s only clinical trial on the effectiveness of cloth masks, fabric coverings which are not specialist surgical masks.
The rates of all infection outcomes were consistently higher for cloth masks than for surgical masks. However, since most of the study’s control group were also wearing surgical masks, it was difficult to determine the performance of a cloth mask versus no mask at all.
Other studies show that cloth masks may provide some protection, but less than
Chughtai said, while some fabrics provide more protection than others.
He conducted a review of 19 studies on cloth masks and results showed that the filtration capacity can improve with a greater number of threads – known as fine mesh – and the number of layers used to make the masks.
“The other use of masks is to stop the spread of the illness by carriers of the virus, referred as ‘source control’, who in the case of coronavirus may well be asymptomatic,” Chughtai said.
“If a high rate of transmission is ongoing in the community, like in the US now, people should use masks, because we know there is a high level of asymptomatic cases. For source control, you can use any mask – even cloth masks are fine.”
A 2013 study conducted by scientists at Cambridge University measured the volume of 0.02 micron particles captured by DIY masks made from household items, ranging from vacuum cleaner bags and tea towels, to pillow cases and scarves. Each captured more than 50 per cent of the particles, the study showed.
“The diameter of [Covid-19] is about 100 nanometres (0.1 micron), it is usually wrapped in respiratory droplets when it leaves the human body, which are about 5 to 10 microns on average, but the droplets could reach up to dozens of microns sometimes, and a cloth mask can filter such big particles,” said Lai, the professor in Taiwan.
Experts warn, however, that cloth coverings should be properly fitted snugly to the face, while they should be washed after use.
Singaporeans have been told to wash their reusable mask with warm soapy water for at least one minute and dry it, preferably in the sun, after each day of use. Prime Minister Lee Hsien Loong said in a national address: “Remember, mask or no mask, you still need to wash your hands, and keep a safe distance away from other people.”
In Hong Kong, after a shortage of masks in February, neighbourhoods lined with stores previously selling stationary or suitcases are now selling masks made in China, Japan, Nepal, Thailand, and Turkey. Some are layered masks, while others are flimsier items emblazoned with cartoon characters.
Cowling at HKU said that a spectrum exists even within the field of surgical masks, which come in various degrees of thickness.
“The ones used in hospitals usually have three layers – outside is waterproof, in the middle is a filter and inside is absorbent material,” Cowling said. “In Hong Kong, you can buy ones which do not have three layers, just one or two layers, they are thinner and you can tell the difference. These would not be as good as the medical grade ones. The filtration performance would be better on the medical grade ones.”
The 2013 study by Cambridge University also found that 89 per cent of 0.2 micron particles were captured by surgical masks, a higher level than any household material tested. This comes with the caveat that not all surgical masks are as robust as others.
“There is a reason why people need to wear surgical masks, even for the general community it works very well,” said Ivan Hung Fan-ngai, chief of the infectious diseases division at HKU. “It has been basically proven by the data in Hong Kong and also in China. I think the World Health Organisation and [US] CDC are now changing their minds because they look at the data and they realise how important surgical masks are.”
At the higher-end of the scale are N95 respirators, or regional variants, such as the Chinese KN95 or the South Korean KF94 and KF99.
The number denotes the percentage of small particles filtered by these products, which are considered to be the gold standard in facial protection, and which experts say should be reserved for essential medical staff.
Theoretically, if these masks are legitimately produced and tested, they should work equally well, experts said. But there are concerns that the Chinese versions are not subject to the same rigorous testing criteria as the versions produced in the US – an issue which has arisen time and again with Chinese-made medical devices and PPE over the course of the pandemic.
Under American regulations, the National Institute for Occupational Safety and Health (NIOSH) under the CDC inspects N95 manufacturers every two years, according to Lai from Chung Shan Medical University. This is called “post-market surveillance” – where a drug or medical device is monitored after being released to ensure standards do not slip.
“NIOSH-approved N95 masks are manufactured under strict inspection, but the problem is we have no idea whether China implements strict post-market surveillance,” added Lai, who has been assisting the Taiwanese CDC in contagion prevention since the outbreak of severe acute respiratory syndrome (Sars) in 2002-2003.
The uncertainty regarding quality control adds to an already complicated picture in the trade of masks and other PPE items, particularly at a time when the volume of Chinese output is so vast and has so many new and untried producers, while demand around the world is so urgent and massive.
In recent weeks, a number of countries including Spain, Ireland, the Netherlands, and Turkey have said that equipment and devices bought from China was substandard. China responded by imposing export restrictions on testing kits and other medical equipment, meaning they must first obtain domestic approval and also meet the requirements of the importing country.
Whether masks fall into these categories or not depends on how they are labelled. If they are labelled as being sold for medical purposes, it does not matter if they are a standard surgical mask or a KN95, they will be treated as a medical device. Otherwise, they will be treated as PPE and face import regulations.
If an exporter in China was to label a surgical mask or KN95 respirator as a medical device, it would encounter different regulations at customs overseas than had it been labelled as PPE. There have been widespread reports of masks being confiscated at American docks because of mislabelling.
Regulation in this area is patchwork – described by some as a “minefield”. It is also dynamic, with countries changing their rules as the crisis evolves. It makes it difficult for buyers and sellers to keep on top of, especially when so many are sourcing or selling medical equipment for the first time.
The complexity of the situation has left some buyers reluctant to enter the Chinese market and raised scepticism over the general quality of
“The most difficult element here is that it is not just a simple case of one size fits all. There are a number of different standards that apply to different types of products,” said Anthony Wilkinson, an intellectual property lawyer at Bird & Bird in Hong Kong, who is also a registered medical practitioner and pharmacist.
“There isn’t a universal acceptance of everything that goes out of every country or into every country. It really requires knowledge of the regulations for your product at the manufacturing end and import end.”