Expect to wear masks until a Covid-19 vaccine is available, a top pandemic advisor to the Government has warned.

Mask use can slow and help stop an outbreak and will be a part of daily life until a vaccine is found, physics professor Shaun Hendy explains.

His comments come as cases from the Auckland cluster, which has infected 149 people to date, slowly decline.

Precautions at Alert Level 2 see mandatory mask-wearing on public transport.

But once the current outbreak is under control, the next question will be about how to manage the future risk – even if New Zealand once again eliminates the virus.

”If we can eliminate the virus now it's a big part of our toolkit for avoiding lockdown again,” he said.

“The lesson from 100 days without transmission was that we did relax. Testing rates declined, some people weren’t going to get tested when they had a cold.

“Mask use can really help prevent another cluster appearing.”

Even with a well-managed border there will always be a risk the virus will get into the community, he said.

“There is no way we can reduce the risk [of community transmission] to zero even with a well-managed border.

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“It's going to be a long period of time, and we have got to be cautious,” he said.

But mask use could have dampened the Auckland cluster, with some cases spreading on public transport, he said.

“It wouldn’t have grown so rapidly [with mask use].

“We are in this for the long haul and masks are one of the tools in use until a vaccine is available,” he said.

Human trials of a frontrunner coronavirus vaccine developed by the University of Oxford began on Monday in the US, with some predicting a reasonably effective vaccine could be in mass production by end of 2021.

Professor Michael Baker said masks won’t be needed routinely if New Zealand reaches elimination status again.

The virus is eliminated when there are 28 days without community transmission, and when health officials can effectively contain any future imported cases from overseas.

“If you are successful in eliminating the virus in New Zealand I think masks will not be needed routinely. The exception could be public transport in winter,” he said.

“The other thing is whether we fine tune the Alert Level System.”

He called for tweaks to the Alert Levels to add a 1.5 and a 2.5 to the system.

“Level 1 is nothing and 2 is quite a bit,” he said.

Alert Level 1.5 should include mask-wearing on public transport, in health care settings and care facilities with no travel in or out of regions experiencing an outbreak.

Mask use on public transport and in residential care facilities should be mandatory at all alert levels in winter, he added.

“We need to put the maximum constraints on virus transmission,” he said.

New Zealand had followed similar approach to many Asian countries by using lockdowns to stamp out the virus.

But whether Auckland’s lockdown had stopped the virus spreading won’t be known for another couple of weeks.