Explainer - Under the red setting of the traffic light system, many New Zealanders will have to adapt to stricter rules around the use of face masks.

In the current setting, all workers who are covered by vaccine mandates are required to wear a medical-grade mask while working in public-facing roles.

But what does 'medical-grade' entail and how does a N95 differ from your common medical mask?

What are the new mask rules?

To minimise the effects of highly transmissible Covid-19 variants like Omicron and Delta, the government has doubled down on the importance of wearing a face covering.

Prime Minister Jacinda Ardern said under the red setting, masks must now be worn at food and drink businesses, close proximity businesses, events and gatherings. While the same exceptions for when people are eating, drinking or exercising still apply.

Face masks prevent or minimise the direct spread of Covid-19 infected particles, and when correctly worn, some masks do a better job than others.

There are three common types of masks, surgical masks, cloth face coverings and heavier-grade respirators like N95 masks. Several factors can impact the effectiveness of a mask including its fit, level of filtration and base material.

With makeshift masks like scarves, bandanas and pulled up t-shirts no longer cutting it - it's now no mask, no service.

According to the World Health Organisation, medical grade blue surgical masks should contain three layers of synthetic material, with filtration layers sandwiched in the middle.

While the packaging of some surgical masks state they are 'not for medical use', Covid-19 Response Minister Chris Hipkins told Checkpoint this is because the masks are not required to be tested for use in hospitals.

"The medical-grade is a shorthand description for that type of mask, there's different conditions and tests that are going to be used in a hospital setting," he said.

Meanwhile, respirators are classed by the standards to which they perform, for example, the N95 mask is held to the US testing requirement of 95 - 99.7 percent filtration efficiency. While the P2 mask is held to the European testing requirements of 94 - 99 percent efficiency.

Disposable KN95 mask vs thin surgical mask. Photo: 123rf

Separating mask from mask

With the Omicron variant in the community, some health experts have called for people to swap out their surgical masks for a N95 or P2 mask.

Director-General of Health Dr Ashley Bloomfield has said that for the general public, a three-layer surgical or cloth mask is acceptable.

However, University of Otago Wellington senior public health researcher Dr Lucy Telfar-Barnard said N95 and P2 masks were the best options because blue surgical masks were more likely to have leakage around the edges.

"I absolutely recommend them, if people are able to access them. I know that they're in short supply at the moment.

"We do need to be making those respirators accessible to people across the population.

"Surgical masks are not good enough in an Omicron outbreak," she said.

University of Auckland aerosol chemist Dr Joel Rindelaub said respirators were the gold standard in protecting against the latest Covid variant.

"They're going to give you the best tight fit and the material is actually going to be able to stop these particles penetrating deep into your lungs," he said.

While an ill-fitting surgical mask can pose a risk of leakage, research by American expert panel ACGIH pandemic task force states that N95 masks are far more effective than surgical or cloth masks, regardless of whether they are effectively fitted or not.

A table supplied by the ACGIH shows that with two people wearing a surgical mask, it could take about 1 hour for a person to become infected with Covid-19, and with two people wearing N95s, the timeframe for Covid-19 to be transmitted is about 25 hours, even without fit-testing of the mask.

Supply and cost issues rule out recommending N95 masks

While respirators have been praised by health experts, low supply and rising costs have put them out of reach for many New Zealanders.

Covid-19 Response Minister Chris Hipkins told Checkpoint that although N95 masks provide superior protection, blue surgical masks are the realistic choice for many.

"The best masks for most people are going to be the medical mask that you can buy from the supermarket, you can buy them in packs of 50 from the supermarket, those are the ones we are recommending people use. You can still use a cloth covering, but there are some cloth coverings of course that are better than others," Hipkins said.

He said there was a 'plentiful supply' of N95 masks for frontline workers in higher-risk areas such as healthcare and border operations.

However, there were a combination of factors that made recommending N95s for the general public difficult, including supply and cost, he said.

While select retailers have N95 masks for sale, demand is expected to quickly outweigh the limited supply with international shipping delays holding up future shipments.

Mitre 10 New Zealand Ltd chief merchandise officer Chris Peak said purchase limits have been put in place for certified respirator masks.

"Surges in demand are causing temporary gaps but stock is being regularly delivered. Some are being set aside to protect team members' health and safety at work and purchase limits have been implemented to help manage demand," he said.

Peak said stock levels of certified masks such as N95 or P2 masks varied across their store network.

Meanwhile, multi-packs of manufacturer 3M's Chinese equivalent to the N95, the KN95, are selling for over $150 on TradeMe.

However, Dr Rindelaub said consumers should avoid purchasing these masks online.

"Try to stay away from the KN-5s because there's data overseas which says over half of these are going to be counterfeit, so, if it doesn't have the certification stamped on the outside, be very wary," he said.

Making do with a surgical mask

If you can't get your hands on an N95, there are various ways of improving the fit and protection of a blue surgical mask, Dr Telfar-Barnard said.

"If you've got a lightweight cloth mask that fits you well you can wear that over the top, or you can use that blue mask cut down to use as a filter in a filter pocket in a cloth mask that fits well.

"You can use a mask brace - there are various arrangements of elastic bands or cut silicon that you can fit over your head. That will hold that close to the face and create that seal all around the cheeks and chin, as well as using the nose wire to make sure it fits well around the nose."

Even a well-fitting cloth mask on its own is better than nothing at all, she said.