An immunologist has warned that while rare, some Kiwis could be reinfected with Covid-19 as new variants continue to emerge.

The possibility appears to be low, however, with the UK recording a reinfection rate of around 10%.

“At the moment, it’s still very rare and it’s still not very clear just why they are getting the second infection,” Malaghan Institute professor Graham Le Gros told Seven Sharp.

It's unknown if reinfection is linked to waning immunity or a variant of Covid-19 which "can come in and infect again", he said.

"We’ve seen overseas in the UK that actually, it's very rare still but you can get the second version of the Omicron virus 60 days after having a good infection with the BA.1 so it’s really tough news for some of us out there that yes, you can get reinfected.”

Le Gros said there are also some cases where people have “this long, malingering infection” where the virus is “no longer viable but they’re still testing positive because there are still parts of the virus being produced”.

He said people can continue to test positive despite no longer being infectious for up to 90 days after the initial infection.

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“The trouble is how do we distinguish that from people who are infectious? We actually have to do a lot of testing to try and prove that they’re actually safe and that’s one of the problems.

"For some of these poor people, yes, they’re not infectious but they’re testing positive and they look infectious but they still are a relatively rare number of people at the moment.”

Herd immunity not the answer

Le Gros said we cannot rely on herd immunity alone as new variants continue to emerge.

“The changing viruses, the changing variants seem to be able to get around our levels of immunity and reinfect us but we are very hopeful that newer, better vaccines will be produced which will be able to boost our immune system and potentially – certainly in the healthy part of the population – really make a strong immunity and really crush the virus so we get an effective level of herd immunity.”

He warned the virus "is not finished with us yet".

"It’s actually going through the first range of variations. It’s trying out how to infect human beings, it’s trying out how to get past the current vaccine regime's level of immunity but it can mix and match with other viruses, it can mix and match with the other variants.”

On Tuesday there were 6380 new Covid-19 community cases in New Zealand.