Unmasking mask efficacy

As Covid-19 restrictions and mandates are relaxed in many parts of Australia, the importance of a well fitted and effective face mask remains high. Masks help protect both the wearer and those around them. But not all masks are created equal.

An expert in virus transmission and sampling biological aerosols, retired Associated Professor Euan Tovey from the Woolcock Institute in Sydney is passionate about masks. While he emphasises that “any mask is better than no mask”, he urges the use of a well fitted ‘gold standard’ mask – technically termed a ‘respirator’ – for the best protection against Covid-19 transmission.

“While we have a disease which is largely but not entirely transmitted via aerosol routes, the most effective sorts of masks are respirators, which are things like KN95s, N95s, or P2s,” he told Retail Pharmacy.

Comparing each of the common masks – cloth, surgical and respirator – shows how efficacy differs between them. The key factors to consider are:

  • How well does the mask filter?
  • How well does it fit? (Gaps reduce efficacy.)
  • How easy/hard is it to breathe through? (Backpressure can create gaps.)

Strengths and weaknesses 

Cloth masks, says Professor Tovey, vary enormously in their capacity to filter.

“Generally, they’re pretty good for big particles, but often not so good for the smaller particles,” he said, describing the filtration as like a “tea-strainer”.

“The virus particles are just too fine – like cigarette smoke, finding every gap, and passing through non-electrostatic filters.”

Fit also varies a lot. Some cloth masks fit snugly against the face, while others (often due to a lack of wire to bridge the nose) leave big gaps.

“We’ve all seen people in the streets wearing [cloth] masks with those great big gaps – you could stick your fingers down either side of their nose – and most of the air and virus particles will be going in and out through that gap.”

Surgical masks made from electrostatic cloth tend to filter pretty well, Professor Tovey adds – “not fantastically, but not too bad” – but often, they don’t fit faces well or are not worn correctly.

“While the filtration is a bit better [than cloth], sometimes the fit is really quite terrible …  and stuff goes through the gaps beside the cheek commonly or under the chin and also around the nose,” he said.

Respirators are also made with electrostatic cloth that attracts and grips onto fine particles. These generally have very good filters and there are several on the market, with the names indicating which country of certification they are using: “N95 is the American one, KN95 is the Chinese one KF94 is the Korean one, P2 is the Australian standard, FFP2 or FFP3 is the European standard,” Professor Tovey said.

As with the other mask options, a poor fit can lessen the efficacy of respirators.

“In a medical context, you’d be fit tested to make sure it doesn’t leak, and you’d find a mask that best matches your face,” Professor Tovey said.

Buyer beware

A principal problem, which occurs with all masks but particularly respirators, is insufficient quality control, he adds.

“This hasn’t been looked at with much attention in Australia,” he said. “A lot of masks on sale here would not pass certification if they were tested according to their local standards. About 50 per cent of imported KN95s would fail a US test.”

He warned that forgeries are also common, especially online.

“There’s no close inspection,” he said. “There’s no website in Australia where you can go to see if what you’re buying would pass a test.”

“We don’t really have good quality control systems,” Professor Tovey added, pointing out that websites in the US have some testing data.

The inability to verify the efficacy of specific masks is a problem for many pharmacists, who may be consulted by customers seeking the best protection.

“I think pharmacies are in a difficult bind because there’s not enough scientific data to allow them to help people make critical decisions on this,” Professor Tovey said. “You can’t say ‘this cloth mask will give you X per cent protection whereas this respirator will give you Y per cent protection’ and I think that’s a problem.

“Most of them do work reasonably well,” he said, “but it’s pretty bizarre that for a medical device which actually has very strict standards, in theory, those standards are not applied in practice in the community.”

Coffee or Covid? 

Despite the confusion around standards and certification, Professor Tovey advises anyone seeking good protection against Covid-19 to opt for a respirator mask.

“If I was going into a situation where I thought I was going to be exposed, why would I choose something that gave me two-fold protection [cloth mask], when I could choose something that gave me 20-fold protection, particularly if other people aren’t wearing masks, and I’m concerned about my own susceptibility?” he said.

“For the price of a cup of coffee per week, you can give yourself pretty good protection against inhaling the aerosol of SARS CoV-2.”

This feature was originally published in the April issue of Retail Pharmacy magazine: retailpharmacymagazine.com.au/magazine/retail-pharmacy-april-2022