New Zealand is being hit by a fifth wave of COVID-19 infections driven by people's immunity to the virus waning, epidemiologist Michael Baker says.
Baker, from the University of Otago, told RNZ's First Up it was "really critical" people took up booster jabs if eligible to make their protection against the virus stronger.
He urged New Zealanders to stay home if sick, despite self-isolation requirements no longer being in place.
"People are more vulnerable and that's driving another wave and it looks like this is the way the virus is going to behave for the foreseeable future - with peaks and troughs - and we're very much in a peak at the moment," Baker told First Up.
He said the rise in infections was due to "waning immunity".
The number of infections in hospital was also the highest since January, he told First Up.
"We actually have to go back right back to January to see this number of copies of the virus in the wastewater across New Zealand," Baker said. "So that's one thing to look at and the other is the hospitalisations - and they're at their highest point for six months."
There were 5872 reported cases of COVID-19 in the week to Monday and 19 people died.
Of those new cases, 2823 were reinfections.
In addition, there were 212 COVID-19 cases in hospitals - five of whom were in intensive care.
The seven-day rolling average of cases was 838.
Unite Against COVID-19, the Government's coronavirus response agency, has reminded Kiwis anyone aged 30 and older is eligible for boosters.
People aged between 16 and 29 who are either high-risk or pregnant are also eligible, it said.
"For most people, including healthy children, the protection provided by the current vaccinations is long-lasting enough to protect against severe COVID illness."