Covid 19 coronavirus Delta outbreak: Mandatory masks 'historic moment for New Zealand'

Mandatory mask wearing is here to stay, a top epidemiologist says, as New Zealanders mask up in the country's first outbreak of the Delta variant.

University of Otago, Wellington, epidemiologist Prof Michael Baker said when mask wearing was made mandatory at businesses open to the public in alert level 4, it was a historic moment for the country.

The new rules represented a huge shift in policy, he said.

While "mass masking" was new here, it would likely become a useful part of New Zealand's response to the pandemic from now.

He did not believe it would always be mandatory to wear a mask in supermarkets, for example, he said.

But mask wearing would become normal as a way to deal with outbreaks.

"It's a tool, that like every other tool, needs to be used appropriately," Prof Baker said.

"We're just recognising that if you've got a respiratory pathogen, the thing that stops it going from one person to another is a mask.

Professor Michael Baker been made a member of the Order of Merit for his services to public health science. Photo / Supplied

"And particularly when you don't have other tools, you don't have vaccines, you've got to really use all these public health measures that are available."

Early on in the pandemic there was an obsession with surfaces, he said, but since then, the evidence emerged that transmission of the virus was almost entirely respiratory.

It was carried through the air, and quite easily.

In many other countries where there had not been the possibility of eliminating the virus mass masking was relied on as a tool to "dampen down" transmission.

Mass masking was important for different reasons than the reasons why high-quality masks were used by health workers, he said.

They were exposed day after day to the virus.

But if everyone wore even a basic mask, they had a very important role in stopping the virus from spreading.

University of Otago clothing and textile sciences Prof Raechel Laing said not all masks were created equal.

Faces varied and cloth masks differed widely. Some had more layers, or different layers, some were single-use and others could be cleaned and reused.

Performance in protection varied, she said. While surgical masks were one size only, they could be pinched close to the nose and ear loops could be twisted to give a closer fit.

The Ministry of Health recommends about four fabric reusable (washable) face masks per person.

Face coverings such as a bandana or scarf were suitable if masks were not an option, the ministry website says.

If worn as a mask, a scarf should be folded three times before it was tied.

Dust masks were not recommended if they had a one-way valve, which would allow droplets to spread if a person coughed or sneezed, it says.