An epidemiologist says those people getting the coronavirus twice is not the normal pattern.
There are reports from China and Japan that a small number of people have recovered from the virus and then tested positive again within weeks.
Otago University professor Michael Baker told Morning Report that was unlikely to be the usual model for the disease.
"This will not be the normal pattern. This will be what we call outliers. There are thousands of people that have now been tested and looked at and there will be a few that have unusual reactions to the virus," he said.
"There are sometimes people who are called super-spreaders who are highly-infectious and with a number of infectious diseases people do seem to have a very long phase of continuing to test positive for the organism than other people.
"So, whether this is a common pattern I think time will tell, but I think it would be an unusual pattern from what we know of the virus."
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The epidemiologist said it was not clear why the World Health Organisation had not declared the illness as a pandemic, other than it being cautious in its approach. Stock markets across the globe plunged this week amid growing concerns over how a pandemic would impact on trade and economic growth.
Baker said the coronavirus should be considered a pandemic and government responses and readiness should reflect that. Australia this week activated its coronavirus emergency response plan and extended its travel ban for a further week. New Zealand also extended its travel ban for Chinese travellers, until 3 March.
"The interesting thing about Australia is now they're using the 'p' word, saying this is a pandemic and it's going to arrive and I think the same message is going out in New Zealand and around the world... It's looked like a pandemic for three or four weeks and is now exactly behaving like a pandemic."
He said New Zealand's emergency plan was based on its existing influenza plan, and was not unlike Australia's approach.
Yesterday, Australia's Prime Minister Scott Morrison said the plan would include cancelling large gatherings, stockpiling medicines, preparing potential feeder clinics in the case of a large outbreak, and if necessary, tougher border control measures. Twenty-three Australians have been diagnosed with the virus.
"New Zealand and Australia have been synchronising approaches to this," Baker said.
"We have the same broad phase, with very similar elements, excluding travel from high-incidence countries and other measures to limit transmission if people arrive with the virus.
"And, what was described in Australia is what is exactly what's happening in New Zealand, moving and planning for the management phase. This is when we have sustained transmission in New Zealand."
Baker said giving exemptions to Chinese students who had signed up to study at universities in New Zealand was a decision for government, but the travel ban had bought health authorities precious time to plan for an eventual outbreak.
"At the moment, Australia and New Zealand have bought quite a bit of time by acting very promptly with this threat and every we get with sustained transmission in New Zealand is another day we can plan.
"I also think psychologically we have to switch to saying 'this is a real thing and it's going to come and it can't be stopped'."
Baker said it was highly likely the Covid-19 would become another winter illness, similar to influenza.
At this stage there are no confirmed cases of Covid-19 in New Zealand, although more than 120 tests have been completed.
The Ministry of Health also issued new advice to health professionals yesterday about identifying possible cases of the virus, by adding Hong Kong, Iran, Italy, Japan, Korea, Singapore and Thailand as countries of a higher level of interest when diagnosing patients.
The Ministry of Foreign Affairs and Trade announced a change to its travel advice for Japan last night, advising New Zealanders to exercise increased caution in Japan due to the outbreak of Covid-19.
Anyone who has visited those countries in the previous two weeks who develops flu-like symptoms should phone Healthline's Covid-19 number 0800 358 5453 or phone their GP.