LONDON (NYTIMES) - A new analysis of 172 studies, funded by the World Health Organisation, confirms what scientists have said for months: N95 and other respirator masks are far superior to surgical or cloth masks in protecting essential medical workers against the coronavirus.
The results, published on Monday (June 1) in The Lancet, make it clear that the WHO and the Centres for Disease Control and Prevention should recommend that essential workers like nurses and emergency responders wear N95 masks, not just surgical masks, experts said.
"It's been disappointing that both the WHO and the CDC have suggested that surgical masks are adequate, and they're clearly not," said David Michaels, a professor at George Washington University who headed the Occupational Safety and Health Administration under then United States president Barack Obama.
"Reliance on surgical masks has no doubt led to many workers being infected," he said.
N95 masks offered 96 per cent protection, the analysis found, while the figure for surgical masks was 77 per cent. The findings are particularly important as the United States moves to reopen the economy, Michaels said.
Workers in healthcare settings are not the only ones at high risk of coronavirus infection: Employees in meatpacking plants and some farms are all also at high risk of coronavirus infection and could benefit from N95 masks, he said.
The WHO has not endorsed universal wearing of masks, although most of its member governments adopted the practice months ago. The organisation's stance has frustrated many public health experts who see masks as a simple, inexpensive and highly effective strategy to help contain the pandemic, especially given that the virus can be transmitted by people who do not know they are ill.
"When there is uncertainty and you don't know everything about a disease, you have to be precautionary, which means you have to assume the worst and provide the best for healthcare workers," said Dr Raina MacIntyre, an epidemiologist at the University of New South Wales in Sydney, who wrote a commentary accompanying the paper.
"This kind of denial, what purpose is it serving - except to harm healthcare workers?" she said.
Previous studies have shown that the universal wearing of masks is effective. If anything, the new study does so based on poorer evidence, said Jeremy Howard, a distinguished research scientist at the University of California, San Francisco, and a co-founder of the global #Masks4All movement.
"This is probably what the WHO needs to change their guidance, even though it shouldn't be," Howard said. "Such is life. It will save lives, so that's good."
The new analysis also suggests that covering the eyes with face shields, goggles and glasses may provide additional safeguards for healthcare workers and people in the community.
The report is among the first to lay out evidence specific to coronaviruses, rather than extrapolating from data on other respiratory viruses.
The coronavirus is thought to spread primarily through droplets expelled when an infected person coughs, sneezes, sings, talks or even breathes. Some infections may also be caused by people touching a contaminated surface and then their mouth, nose or eyes.
Study after study has indicated that the virus can also spread via tiny droplets less than 5 microns, called aerosols. (A micron equals one millionth of a meter.) But the WHO has so far not acknowledged this risk and has not backed the universal use of masks.
"There's this fear around saying airborne - but that's what it is," MacIntyre said.
A recent review in the journal Science took direct aim at the WHO's reluctance on this issue, saying the organisation's recommendations for physical distancing and hand washing were based on studies "carried out in the 1930s".
The CDC did not recommend masks till April 3. Even now, its guidance says surgical masks offer enough protection for healthcare workers unless they are involved in procedures that produce aerosols.
The CDC initially recommended N95 masks for all healthcare personnel. MacIntyre said the agency later downgraded its recommendations because of a shortage of N95 masks and personal protective equipment.
"Guidelines should be based on evidence, not on supplies," she said. "It's like telling an army, 'Oh sorry, we've run out of guns, just take these bows and arrows and face the enemy.'"
She noted that N95 masks were inexpensive to produce and that other countries, including Australia, had repurposed existing manufacturing facilities to make the masks.
"We're not talking about making a space shuttle," she said. "We're talking about making a straightforward piece of equipment that's quite cheap to manufacture."
A CDC spokesman was unable to address the Lancet study but said the agency is constantly evaluating new science and "adjusts its guidance accordingly."
