Study will investigate effectiveness of Pfizer

AUCKLAND: New Zealand confronted Omicron as one of the most vaccinated populations on the planet — so what difference did that make in blunting the worst impacts?

This is the focus of a new study that explores the effectiveness of multiple doses of the Pfizer vaccine against Omicron, in what was also one of the world’s few ‘‘infectionnaive’’ populations.

Study leaders Dr Anna Howe and Dr Matt Hobbs also aimed to answer another critical question — what protection the vaccine gave Maori, Pasifika and other highrisk groups.

By the time the Omicron outbreak forced the whole of New

Zealand into the Red traffic light setting on January 23, about 93% of the eligible adult population — 3,910,251 people — had already received at least two doses of Pfizer’s Comirnaty vaccine.

On top of that, 974,784 people had been boosted and more than 36,000 had received their third primary doses, giving the country one of the highest levels of coverage anywhere in the world.

By contrast, New Zealand had only confirmed 15,175 cases of Covid19 — most of those from the Aucklandcentred Delta outbreak that began five months before.

Some 1.7 million confirmed cases later, modellers estimate the true proportion of infection could amount to up to twothirds of the population — it is clear that high vaccination rate was not enough to hold back the quickspreading Omicron’s tide.

However, as vaccinologists have pointed out to the Herald, there’s much to suggest vaccination played a big part in giving New Zealand one of the lowest case fatality rates in the world — by helping slash the risk of severe sickness, hospitalisation and death.

As of Friday, the Ministry of Health had recorded 1245 deaths where Covid19 had been formally coded as the underlying cause, along with 13,443 hospitalisations — 484 of which required ICU care.

While experts have said most New Zealanders should be relatively well shielded against the very worst outcomes of Omicron for now — thanks to vaccination and ‘‘hybrid’’ immunity gained from natural exposure to it — knowing the vaccine’s impact was nonetheless important.

‘‘In the highcoverage postOmicron environment, some data sources showing only numbers of cases and hospitalisations in vaccinated and unvaccinated people can allow misleading interpretations, such as vaccination increasing disease risk,’’ Dr Howe said.

‘‘Internationally, there have been challenges in vaccine effectiveness analyses and uncertain applicability to the infectionnaive New Zealand population, particularly Maori and Pasifika.’’

Although there had now been many effectiveness studies of the vaccine, few had been carried out during Omicron’s dominance — and there had been none conducted in a population with such a unique immunity profile as ours, she said.

‘‘This information is vital for equitable immunisation policy decisions going forward for New Zealand.’’

The team would be drawing on health data to measure what the overall number of vaccine doses, as well as the timing of those doses, generally meant for vaccine effectiveness.

Naturally, that was not a straightforward undertaking in an ongoing pandemic, and similar overseas research efforts have repeatedly run up against tricky methodological issues.

But recently, a World Health Organisation advisory group set out steps on how to get a clearer measure of effectiveness, which the New Zealand team would align their study with.

‘‘This project will use a layered approach, starting with validated data on severe disease — hospitalisation, ICU admission and death — and vaccine coverage in descriptive analyses,’’ Dr Hobbs said.

‘‘We’ll then use these foundations to generate highquality, reliable vaccine effectiveness estimates with appropriate statistical adjustment.

‘‘Our findings will provide accurate data that accounts for local context, as trustworthy local data presented in a relatable way is vital for community trust and confidence.’’

The study would also put special focus on key subgroups, including Maori and Pasifika, by age group and presence of medical risk factors.