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.
-RNZ
