Masks key to preventing virus – experts

Washington – As new, more transmissible variants of the coronavirus spread, experts say it’s time to consider using a medical-grade respirator, or wearing a surgical and cloth mask together.

Scientists have agreed for some time the main way the virus is spread is through the air, rather than surfaces, and there’s growing evidence that small droplets from ordinary breathing and speech that can travel many metres are a common mode of transmission.

Added to this is the greater contagiousness of emerging variants, like B.1.1.7, which takes a smaller viral load to cause symptomatic Covid-19 compared to the more common strain.

Back when authorities first recommended people wear face coverings, proper masks were in extremely short supply and the public was encouraged to fashion makeshift solutions out of T-shirts or bandannas. But these are far from ideal.

Linsey Marr, a professor of civil and environmental engineering at Virginia Tech, who studies airborne disease transmission, said: “How well a mask works depends on two things: filtration and fit.

“Good filtration removes as many particles as possible, and a good fit means that there are no leaks around the sides of your mask, where air – and viruses – can leak through,” she said, adding even a small gap could lead to a 50% reduction in performance.

The best materials for blocking small particles include nonwoven polypropylene, which is used to make N95s and many surgical-type masks, and the Hepa filters in planes. Among fabrics, tightly woven cotton works best, she added.

“If you wear a cloth mask, choose one that has multiple layers, ideally one with a pocket that you can slip a good filter material into,” said Marr. “Or you can double mask by wearing a surgical-type mask with a tight-fitting cloth mask over it.”

Surgical masks are made of material that filters things out well, but they tend to be loose, so adding a cloth mask on top holds down the edges and reduces leaks.

Adding an additional layer improves filtration – if one layer traps 50% of all particles, combining two gets to 75%.

But, she added: “We do not recommend wearing more than two masks. Adding more layers proves diminishing returns and can compromise breathability.

“It must remain easy to breathe through the layers; otherwise, air is more likely to leak in around the sides of the mask.”

Masks that have a metal nose bridge help ensure a snug fit, as do straps that tighten around the head, not just the ears. Braces that improve the fit of surgical masks are now available on the market.

“You should feel the mask sucking inward when you breathe in,” said Marr. –