Rod Jackson: Omicron outbreak – our time to vaccinate is running out

OPINION

Before Omicron, vaccinated New Zealanders played a big role in protecting the unvaccinated against Covid-19, as they have often done with other infectious diseases for decades.

While the contagiousness of Delta meant that herd immunity (a sufficient level of immunity in the population – the herd – to stamp out transmission) was ultimately not possible, high levels of vaccination certainly bought us time to implement other interventions.

Indeed, along with MIQ, contact tracing, masking and other public health measures, we almost squashed the last Delta outbreak.

Omicron is different. Whereas two doses of vaccine were highly effective at preventing both infection (about 75 per cent compared to the unvaccinated) and severe disease (about 90-95 per cent) from Delta, two doses are much less effective at preventing infection from Omicron (only about 30 per cent).

Fortunately for the vaccinated, two doses are still very effective at preventing severe disease (about 70 per cent). Moreover, the booster raises protection against severe disease to about 90 per cent, as well as significantly reducing risk of infection by up to about 70 per cent.

But this means that vaccinated Kiwis who are not boosted – still the majority of vaccinated New Zealanders today – will provide less protection to the unvaccinated from Omicron and so most unvaccinated are going to get infected within the next few months.

Importantly, but not widely understood, Omicron will be more harmful than Delta would have been for the unvaccinated New Zealand population.

The best estimates of Omicron severity after adjusting for immunity from vaccination or infection, suggest it is only about 25 per cent less severe than Delta for each individual who is infected. Clinically, this is an insignificant reduction in severity.

However, what makes Omicron worse than Delta for unvaccinated New Zealanders is that almost all of them will be infected in the next few months. A significant proportion would have escaped Delta, at least until new effective antiviral drugs became widely available.

Looking at recent international trends can be deceptive. Unlike in most of the world, very few unvaccinated New Zealanders have already been infected, so they have no immunity.

That’s why about 70 people a day are currently being killed by Covid-19 in Australia. As in New Zealand, most unvaccinated Australians have no immunity against Covid-19, because like us, they largely kept Covid-19 out until Omicron arrived.

So, right now is the right time for the remaining vaccine-hesitant to get vaccinated, particularly if you are older, have other health issues, are overweight. Unvaccinated Māori and Pacific people are at very high risk of severe disease and death. There are probably only a few weeks left before it’s too late to get vaccine-induced protection, and even one dose is better than none.

If you follow the rules, you might buy sufficient time to get a second dose and even a booster.

If you are vaccinated, remember that boosters will also increase your protection against severe disease from about 70 per cent to 90 per cent or more compared with not being vaccinated.

Vaccination is still by far the best approach to reducing the speed of spread of Omicron and its impact on our health services, our food supply and our other businesses.

Worldwide, there have been more cases of Omicron reported in the last 10 weeks than all cases of Covid-19 reported last year.

Covid-19 has killed an estimated 15-20 million people (the officially reported five to six million deaths is known to hugely underestimate the real number of deaths).

Infection has provided some immunity to the many hundreds of millions, who were fortunate to survive, but many millions are still suffering long Covid and we have no idea how many will recover.

You don’t want to get infected if at all possible.

To date, about nine million doses of vaccine have provided the majority of New Zealanders with significant immunity and there have been two likely vaccine-related deaths.

In contrast, we have had fewer than 20,000 Covid-19 infections in New Zealand so far and this small number of infections has already caused more than 50 deaths.

Do the maths, then please go and get vaccinated. February is probably the last chance unvaccinated Kiwis have to benefit from vaccination.

• Rod Jackson is an epidemiologist at Auckland University.

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