About 14,000 New Zealanders are known to have been infected with Covid-19 twice and Ministry of Health figures show 183 people have had the virus three times.
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The ministry said about two-thirds of the reinfections happened between one and three months after a first infection.
The figures related only to those actually reporting their positive tests so there would likely have been more.
The number would almost certainly increase as people's immunity from the booster or previous infections declined over time.
Te Whatu Ora's director of population health for Counties Manukau, Gary Jackson, said new variants were also playing a part as they were able to evade immunity acquired from earlier variants.
"But Omicron can even evade itself so after about six months you have got a reasonable chance of catching the same strain," he said.
It was now about three months since the big Omicron peaks of March and April and that could mean a surge in the numbers getting reinfected, he said.
That meant it was important to keep being careful and taking protective measures like wearing masks in high risk settings and staying home if sick, he said.
Getting the fourth booster would also help, Jackson said.
A Ministry of Health spokesperson said there was still a lot to learn about Covid-19 reinfection but there was no evidence yet to suggest people would get a more severe infection the second time.
Health experts have said getting reinfected increased the chances of experiencing complications like Long Covid.
