Covid 19 Omicron: How often will I need a Covid jab?

Many Kiwis may not need a frequent jab to guard against Covid-19, an expert says - but vulnerable people still might need a boost as often as every six months.

Just how often we'll need to get a jab remains one of the biggest questions hanging over a pandemic that's far from finished, with scientists still learning about what immunity we're gaining from boosting and infection.

The Government is still mulling whether to offer a fourth dose to the vulnerable – something Australia and other countries are moving to do – and in the meantime, its focus is on lifting coverage rates.

Anyone aged over 16 who's completed their primary course – that's two doses for most people – at least three months ago is eligible for a booster, but further shots aren't currently available.

"While at this stage it is too early to say what the programme may look like in future, we will continue to monitor and adapt our approach as needed," National Immunisation Programme director Astrid Koornneef said.

Experts told the Herald that, barring no dramatic turn in the pandemic, we shouldn't expect to have to top ourselves up as quickly as we did with boosting after the second shot.

"What we know is that, six months post-boosting, protection against severe disease is still good – so it doesn't look like everybody is going to need to rapidly be boosted," said Dr Nikki Turner, director of the University of Auckland's Immunisation Advisory Centre.

Experts say it's unlikely most Kiwis will need to boost themselves against Covid-19 more than once a year - if not less frequently. Photo / Bevan Conley

Because vaccine-acquired immunity could wane – and particularly among older people, as one recent New Zealand study highlighted – Turner suggested it might be that high-risk groups needed boosting more often, and perhaps every six months.

"I don't think there'd [need to be] an annual jab for everybody at this stage: there's potential, but only in that it could tie in with a flu vaccine for high-risk groups."

While vaccines have generally performed more poorly against Omicron than Delta and the original virus strain, studies have shown how getting a booster – as about 71 per cent of eligible Kiwis have - greatly slashed the risk of severe sickness and death.

One recent study, drawing on data from 2.2 million people in Qatar, indicated that boosters were around 76 per cent effective at protecting Omicron-infected people against hospitalisation and death.

"This might not totally protect against getting any Omicron infection, but it should stand them in very good stead against severe illness or needing to be hospitalised, which is what we care about the most."

Turner also noted that many Kiwis would have "hybrid immunity" from being boosted and exposed to the virus itself - modellers estimate infections in this Omicron wave might cover half the population – giving the country a degree of background immunity.

In February, researchers reported that, while having been infected with an earlier variant produced an immune response about 90 per cent effective against Delta, that fell to just 56 per cent against Omicron.

Slightly more encouraging was the fact previous Covid-19 infection did offer a relatively high level of protection against severe, critical or fatal disease, with the same researchers reporting effectiveness of 100 and 78 per cent against Delta and Omicron respectively.

Turner said: "We now have a strategy to prevent severe disease, and at this stage, for the majority of the community, vaccination plus or minus catching the disease is giving reasonable protection against that."

"It doesn't look like everybody is going to need to rapidly be boosted," Immunisation Advisory Centre director Dr Nikki Turner says. Photo / Mark Mitchell

Immunologist and Malaghan Institute director Professor Graham Le Gros similarly expected most of us wouldn't need frequent jabs.

"At a population level, I think a booster perhaps once a year is what we could handle," he said.

"And we could nuance this with top-ups for special groups like those at risk – like much older people, those with co-morbidities, or those about to have cancer therapy – and perhaps people travelling overseas who want to have maximum immunity."

Vaccine makers have been pushing toward a joint Covid-flu shot, along with a pan-coronavirus vaccine designed to target current and future forms of the virus.

But Le Gros, whose colleagues plan to trial a Kiwi-made Covid-19 booster in people by the end of the year, was sceptical that an all-in-one coronavirus shot could work.

"The idea of making a pan-coronavirus vaccine ... I think it's going to be too difficult, as too many variants and too many proteins involved means it won't be stable or reliable enough."

For the time being, Otago University epidemiologist Professor Michael Baker saw potential to generally offer Covid-19 boosters alongside flu vaccines each year.

"An annual regime where you go out and get your two jabs makes quite a bit of sense; from a number of different trials, we now know they don't interfere with each other."

Baker saw the three biggest unknowns facing future vaccination roll-outs as how much vaccine-acquired immunity waned, what the next pandemic-driving variant would look like, and to what degree vaccination protected against Long Covid.

"If we decide we're only going to have an annual top-up, and breakthrough infections become more likely as a result, does that predispose you to Long Covid?" he said.

"If it does, we all might well be racing along to get a vaccine more often, even if we're not in a high-risk group."

Yesterday, officials reported another 8270 new Covid-19 cases in the community, along with five deaths – bringing the total number of virus-linked mortalities since the pandemic began to 602.

Meanwhile, Prime Minister Jacinda Ardern's first overseas trip in over two years has already hit a snag - with three of the 50-strong delegation testing positive for Covid following a PCR test on Monday night.