'No one alive's been through a pandemic like this' - infectious disease expert Michael Baker

An expert in infectious diseases says there has been a "sigh of relief" from the health sector after the Government imposed strict new travel measures over the weekend to stop the spread of COVID-19.

Anyone arriving in New Zealand after 1am on Monday will now need to self-isolate apart from people from Pacific islands with no confirmed virus cases. All cruise ships will be banned from entering the country until at least June 30.

"No one alive today has really been through a pandemic like this where we have to think about all these new approaches," Professor Michael Baker of Otago University's department of public health told Magic Talk on Monday.

"I think there was this collective sigh of relief from the entire health sector that we're going down this containment path. So I think that's really good for New Zealand."

Prof Baker said if nothing is done to contain the virus' spread, millions of people could end up dying.

"The reason it's a problem at the more severe end [is that] about one percent of people are dying from the infection. So, unfortunately, it means if it sweeps around the globe and infects maybe 50 percent of the world's population over the next one to two years, maybe more, and one percent die from it, that's tens of millions of people dying across the globe and that's obviously a huge tragedy.

"That's why everyone's so worried about this infection."

Earlier on Monday Prime Minister Jacinda Ardern said the Government could deport overseas travellers who fail to self-isolate after arriving in the country. 

Her comments came after Newshub spoke to a number of European backpackers arriving on a flight from Australia who said they planned to travel around the country in a campervan without taking particular steps to self-isolate.

Prof Baker said the Health Act did allow for forcibly enforcing quarantine if people weren't complying with the rules, but travellers in a campervan might not necessarily be putting others in danger.

"If people are blatantly disregarding it that's really irresponsible. But what I would say is if you've got a family group that has arrived from, say Melbourne, they're in their campervan as a family unit, they're travelling around, that is a form of self-isolation if they're not having contact with other people.

"The essence is contact with people - it doesn't mean you have to sit in one spot."

Developing immunity from COVID-19

Prof Baker said around 30 or 40 groups around the world were making progress on developing a vaccine for the virus.

"The problem is the next phase of trials - you need a lot more people and you need to ideally test it on a population who are exposed to the virus to see if it actually works, so that's the real problem, testing it more widely."

After that, there is the challenge of "scaling it up" and producing it great quantities for the billions of people around the world who need it.

Although for most people it's like a bad flu, "at the extreme end it isn't - it's a lethal infection," Prof Baker said.

"Every winter in New Zealand we have about 500 people dying from seasonal flu, but this is like if you imagine stacking up 20 or 30 flu seasons all on top of each other all arriving at once. It's very severe and it would overwhelm our health system."  

Most people who contract the illness and recover would probably be immune from catching it a second time, Prof Baker said.

"If that's not the case the world will be in trouble, because then vaccines won't work, for instance. So we have to assume that this virus will behave like pretty much every other virus we know where you get immunity - and that's what our immune system is for, that's why we evolved to have it. It would be very surprising if there wasn't a good immune response that protects people from subsequent protections."

Another year until it's 'business as usual' in New Zealand

Prof Baker says it won't be "business as usual...possibly for another year" in New Zealand, and globally for about two years.

"This is quite a slow-moving pandemic," he told Magic Talk. 

"The pandemic wave will take months. If you did nothing to contain it... if it washed over the whole world this pandemic wave would take at least eight months, maybe a year to work its way around the globe." 

The fact countries are trying to contain it means it will have less impact but will also be more drawn out, he said.

"So we have to just get used to a new way of doing business."