Several studies indicate waning immunity six months on from becoming fully vaccinated, but there isn't a strong case to start booster shots for the 40,000 border workers and their whānau who were at the front of the rollout queue.
That's because even if there was conclusive evidence that immunity decreased to a level that touched on the dangerous spectrum, those who should be at the front of the booster queue are those who are older or who have underlying health conditions.
Such people in south Auckland didn't start getting their first doses until March at the earliest, while the vaccine doors didn't open for those outside south Auckland until May.
Border workers and their whānau were the first cabs off the rank in late February, and they will start passing the six-month window after the second dose from November.
But most of them will have had a stronger and longer lasting immune response from the vaccine, so there is less of a need to start giving them boosters.
Boosters certainly boost
The key question for the Government has been this: why not start giving boosters, just in case the waning immunity puts communities at unnecessary risk?
There is adequate supply, and has been since July - except for the early weeks of the Delta outbreak in late August and early September when there was a rush on vaccine clinics.
Today there are well over 1 million doses in stock, even if the most recent Ministry of Health data doesn't include the additional 750,000 doses that were shipped from Spain and Denmark.
While the need for boosters is contested, two aspects are clear: a booster shot definitely increases immunity, but two shots of the Pfizer vaccine continues to provide excellent protection beyond six months against severe disease, hospitalisation and death.
The Ministry of Health's plan continues to be "watch this space", which vaccinologist Helen Petousis-Harris says is a "reasonable" stance.
"What we know about boosters is that they induce a fabulous response, which is much higher and more diverse than what you achieve after your second dose. It's also likely to provide a longer duration of sustained antibodies for a while.
"We've also got the data from Israel that shows using a booster for those who are the oldest and the frailest has dampened down those breakthrough cases."
A study of 4868 people in Israel found a "substantially decreased" immune response, especially among men, six months after the second Pfizer dose among people aged 65 and over, and among the immunosuppressed.
A similar result followed an eight-month study in Qatar, which concluded that immunity "appeared to wane rapidly following its peak after the second dose, but protection against hospitalisation and death persisted at a robust level for six months after the second dose".
These recent studies follow many others in previous months indicating waning immunity, but experts have said that definitive conclusions are difficult as there are many variables, such as what restrictions were in place.
An article in the Lancet last month said of these "observational studies": "None of these studies has provided credible evidence of substantially declining protection against severe disease, even when there appear to be declines over time in vaccine efficacy against symptomatic disease."
The authors added: "Even if boosting were eventually shown to decrease the medium-term risk of serious disease, current vaccine supplies could save more lives if used in previously unvaccinated populations than if used as boosters in vaccinated populations."
This accords with the World Health Organisation's view that administering booster shots when many people in parts of the developing world are yet to get a single dose is morally abhorrent.
Similarly, the European Centre for Disease Prevention and Control found last month "no urgent need of a booster shot" because a third of adults in the EU are yet to have had both doses of the vaccine.
Looking at boosters through a New Zealand prism
A similar argument can be made in New Zealand, where 19 per cent of the eligible population are still to get a single dose.
Petousis-Harris, who has been in Auckland's lockdown, said administering booster shots should only be considered if it can be done in a way that didn't disrupt efforts to vaccinate hard-to-reach communities.
"You wouldn't want it to be detrimental on where we've got to get to before we're allowed back out to play."
She added that if it could be done without disrupting those efforts, then why not?
"If they've got the resources and the availability of the people, and if it wasn't going to have any impact on that work, I don't see why that would be a problem at all."
But boosting border workers shouldn't be the priority, not only because the risk of a leak from the border shrinks as more of the eligible population becomes vaccinated; almost 53 per cent are now fully vaccinated, with a further 28 per cent with one dose.
"They aren't your very frailest, most elderly, most unwell people. They are generally quite healthy people who will have, on average, a much more sustained immune response than those other groups," she said.
"I don't think there's anything anywhere in the world to indicate that you would be unduly worried about them at this point."
The booster issue could still be turned upside down by the emergence of "variant X that hasn't come yet but we know it will".
"Whether it's able to evade our immunity it always on the cards. If we do want a booster, we want the latest and greatest."
That's one of the issues that director-general Ashley Bloomfield has said is under negotiation with Pfizer - whether the vaccine is likely to be tweaked to take account for whatever variant is dominant, or a future variant.
The Ministry of Health said no decisions had been made on a booster shot.
"At this stage, there is currently insufficient evidence to support widespread need for a third dose.
"However the emerging evidence is being carefully monitored and we expect to have more certainty on this over the coming months. "
Petousis-Harris said the time will come for a booster.
"When the right time is is still up for grabs."
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