The Covid immunity cycle: Why catching the virus is basically our new booster

Thursday, 12 March 2026

The Media Council has upheld a complaint about this article. You can read a summary of the ruling here.

This story initially said there were 19 deaths with Covid-19 the past week. This is incorrect. Weekly Covid deaths are no longer reported like they were during the pandemic.

Protecting ourselves against Covid seems to have fallen a long way down the priority list for many Kiwis. But cases are rising and we’re in our ninth wave of the virus. So should we be doing more to stop it? Or just let it rip? Lloyd Burr takes a look.

I’m sitting in the pharmacy in Woolworths Ponsonby about to get a Covid booster jab. Why? Because I’ve had Covid a few times, it sucks, and I don’t ever want to feel that crook again.

“How many Covid vaccinations have you had over the years?” asks the Pharmacist. *Crickets*. I actually had no idea. I think this is my sixth one? Maybe seventh.

He tells me it’s been the busiest day yet, with so many people booking upon hearing news of a new wave of cases. That’s one of the reasons I booked in too.

It’s the ninth wave of Covid in New Zealand since Omicron arrived here and started spreading. A ‘wave’ is when there’s a surge in community infections - the current one can be seen on Health NZ’s case tracker.

Is this the new normal? Should we expect this every year? Or is it happening because New Zealand’s collective immunity has waned because of a low infection rate and vaccine uptake?

Let’s bring in an expert: Professor Michael Plank from the University of Canterbury.

It’s more of a ripple than a wave

Describing it as a ‘wave’ creates an image of large swathes of people being swept away with Covid infections. But this wave is not as extreme as that.

“It's a small wave by comparison to what we saw during the pandemic,” Plank says. “It's a ripple, but a ripple can still mean you have a large number of people getting sick, needing time off work, and that sort of thing”.

Why is it happening now?

One of the factors is herd immunity - which is our combined ability to fight off variants of the virus.

“Our immunity is in a cycle. It will dip, and then it will increase over time,” says Plank. “So it's not that we're going to lose it entirely but it will go through those dips and peaks.

“What we're seeing in this wave is a number of people getting infected, causing the level of immunity in the population to get a boost.

“But over time, that immunity wanes, possibly new variants come along which bypass that immunity and eventually you're in a situation where the immunity has dropped to a point that the virus can spread again and you get another wave,” he says.

Variant soup

First it was the Alpha variant, then Beta and Gamma. The ones New Zealand is most familiar with are Delta and Omicron which have gone on to mutate into sub-variants.

So what’s dominating New Zealand at the moment? A soup of them all.

“There's a bit of a soup of different variants,” Plank explains. “There isn't one that's clearly driving the wave like in our previous waves”.

“It’s a sign the immunity we have in the population has broadened out, is more of a soup of variants and probably indicates that waning immunity is playing a role,” Plank says.

The ‘back to school’ factor

Another reason for the current surge in cases can be attributed to education.

“It’s the back to school and back to university time of year which is probably giving the virus a bit of a helping hand. Those conditions allow respiratory viruses like Covid to spread more easily.

“There’s more people in school classrooms, in lecture theatres, back at work, and so on. That just makes more opportunities for the virus to spread,” Plank says.

The Flu has a season, Covid doesn’t (yet)

Professor Plank points out that influenza has a pretty consistent season in that is spreads during the winter with infections peaking in July each year.

“But Covid is a bit less predictable in terms of the timing,” he reveals. “It is possible we end up with more than one wave per year. We might have a winter wave, and we might have a back to school wave”

“Covid is probably a little bit more transmissible than influenza too, and that tends to indicate more than one wave per year,” Planks says.

“It's a bit unpredictable in its timing, but it's here to stay,” he adds.

(By the way if you haven’t seen it yet this chatbot below is powered by the latest report from the Royal Commission of Inquiry)

Do we still need to bother with vaccine boosters?

If our combined immunity comes in waves - or ripples - is there a need to get a booster shot of the vaccine from the pharmacy or doctor?

“Yes,” says Plank. “We do have tools to reduce the impact of this virus, and the vaccine is the best one of those so getting a vaccine is a good idea”

“A vaccine will reduce your risk of getting seriously ill, it will reduce your risk of catching the virus, and passing it on to other people. So that's a win,” he says.

“It's not perfect because over months, the protection you get from that vaccine will reduce,” Plank says.

His final advice: “If you have respiratory symptoms, if you're coughing and spluttering, it's a good idea to stay home, and stay away from other people to reduce the spread,” Plank says.

This story initially said there were 19 deaths with Covid-19 the past week. This is incorrect. Weekly Covid deaths are no longer reported like they were during the pandemic.