An epidemiologist warns Covid-19 reinfections – already making up a quarter of reported cases – will keep rising as New Zealand’s latest Omicron wave pushes case counts to levels not seen in months.

But Otago University’s Professor Michael Baker adds there’s also some worrying unknowns about the impact of reinfection, and is warning Kiwis to avoid another bout with a virus that’s running rampant over the festive season.

There have been 34,528 new community cases of Covid-19 in the past week and 40 deaths attributed to the virus, the Ministry of Health reported today.

As at yesterday, there were 3900 reported cases, and the seven-day rolling average stood at 4926 - the highest counts seen since August.

There were also 418 people in hospital at midnight, the highest number recorded since August 21.

Reinfections accounted for about a quarter of reported cases, which reflected only a subset of New Zealand’s overall picture of Covid-19 infection.

Speaking ahead of the latest release of weekly Covid-19 case numbers today, Baker said reinfections would naturally account for an increasing proportion of all cases the longer the virus was able to circulate in our communities.

Modellers estimate that at least two thirds of Kiwis – and perhaps eight in 10 of us – have now had the coronavirus.

“Eventually, virtually all infections – except in very young children – will probably be reinfections,” Baker said.

“It’s possible there may be a tiny minority of people able to avoid infection by very rigorous efforts, or there may be others who have very powerful innate immunity, and for various reasons won’t have symptomatic illness, and won’t get tested.”

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Covid-19 modeller Dr Dion O’Neale told the Herald he’d expect the rate of reinfection to be “at least” as high as a quarter of all cases – and to probably increase.

“The reported rate will likely be an underestimate since for people to be noted as a reinfection in official data, they have to have reported their confirmed infection both times,” said O’Neale, of Covid-19 Modelling Aotearoa.

“If they miss reporting either one of those infections, then the reinfection will get missed.”

Because the current wave was being driven by a mix of new subvariants able to dodge protection people had from prior infections, O’Neale said the reinfection rate would continue to climb.

“This means that compared with when BA4/5 were the only variants around, people who had a bit of protection against those older variants due to prior infection will have less immunity to these new variants and are more likely to be reinfected, than they were say a month or two ago.”

Baker said researchers were still trying to answer critical questions around reinfection.

But he pointed to a major US study that found all of the negative effects of infection could occur with each reinfection.

“These were people who’ve been reinfected several times, so I think that’s very worrying.”

Baker again encouraged people arranging Christmas functions to choose venues that were outdoors or otherwise well-ventilated, and to stay away and get tested if experiencing any symptoms.