Covid-19 Response Minister Chris Hipkins has defended the recommendation that people use disposable surgical or medical grade masks as opposed to N95s, saying it is an issue of practicality. 

The government today announced it is tightening rules for mask use under the 'red' traffic light setting. Masks must now be worn in all food and drink venues, close-proximity businesses, events and gatherings. The mask exception for eating, drinking and exercising still stands.

Hipkins told Checkpoint the most important point was that they were encouraging people to wear proper masks that covered their mouth and nose, as opposed to people just pulling their T-shirts over their face. 

"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, these 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.

"The paper face coverings are more effective than the fabric face coverings, there are some fabric face coverings that are very good, however, the ones that have several layers and then often have a filter, those are still good masks."

There were a combination of factors that made recommending N95s difficult, including supply and cost, he said.

"They're more expensive and they've also got to be fit-tested, so if you don't have the right fit for your N95 mask, it's not necessarily a better mask than using one of the hospital grade masks you can buy from the supermarket."

However, 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 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.

Hipkins said that needed to be put into the context of the current issues that were considered, "including practicality, supply and cost".

"We've got to make sure that people can comply .... [and we know] with those medical masks, they're readily available from the supermarket and other places so people can actually use them."

While he said there was enough N95 mask supply for frontline workers, "if we were to extend that to the wider public, we do know that for example the supermarkets can source medical masks relatively easily, [but it] would be more difficult for them to be sourcing N95 masks.

"There are international supply constraints around that. And also if you are looking at the proportion of benefit to risk, the most important thing we can do at the moment is encourage people to wear masks properly, whatever type of masks they are wearing."

Hipkins said he was also having discussions with the Ministry of Education around supply of masks in school settings.

"We're also making sure we're working with community organisations, food banks and others to make sure that masks are available to those who might not otherwise be able to access them."