NZ may be able to stamp out Delta before Omicron arrives

Predictions of rampant Covid-19 once Auckland’s borders reopened have not come to pass. Delta case numbers are incredibly low, so much so that eliminating the variant may be within reach.

New Zealand recorded 14 community cases yesterday, which means we’re seeing a seven-day average below 30.

The number of cases in the community on Monday (27) was actually lower than the number of cases at the border (33).

The August 2021 outbreak has led to more than 11,000 Covid-19 cases. Only some 720 are now classified as ‘‘active’’.

According to modelling from Dr Christopher Billington of Melbourne University the R number in New Zealand is now well below 1. This is the average number of people an infected person will pass the virus on to. Above 1 means an outbreak is growing. Below 1 means it’s dying out.

At first glance, this seems extraordinary. Are we just missing cases though? UK data, for example, suggests only 1 in 3.5 infections are recorded as a case. This could be what’s playing out in Aotearoa, but we can’t know for sure, Professor Michael Plank says.

Over Christmas, testing numbers in New Zealand fell off considerably. About 13,000 daily tests have been administered on average over the past week. Some 30,000 people were being tested at times late last year.

Our World in Data suggests: ‘‘Countries that do very few tests per confirmed case are unlikely to be testing widely enough to find all cases. The WHO has suggested 10 to 30 tests per confirmed case as a general benchmark of adequate testing.’’

We’re doing more than 200 tests per case found. This is good news.

The number of people hospitalised with Covid-19 has also continued to fall, as has the number of people in ICU. This is an excellent sign, Professor Michael Baker says. And on both Monday and yesterday, the Ministry of Health said there were no surprising wastewater finds. It is also encouraging that the percentage of people who test positive remains fairly low.

Professor Nick Wilson also said it appeared that contact-tracing teams had been successful in stamping out infections as soon as they took hold.

But the key reason Delta has been kept in check is the exceptionally high vaccination rate, Plank says.

Why does it even matter if Omicron is coming?

You might think the seemingly impending arrival of Omicron makes New Zealand’s current case numbers a bit of a sideshow.

Yes, the emergence of Omicron has changed the dynamics of the pandemic but the Delta variant remains a threat.

Keep in mind that a number of countries were seeing significant Delta outbreaks when the more transmissible but less severe Omicron strain arrived.

This has created a confusing picture where it’s tricky to untangle whether it’s Omicron or Delta sending people to hospitals or ICUs.

NSW Health, for instance, recently released a statement which suggested 74 per cent of ICU admissions since mid-December were for Delta.

On Sunday, ABC in Australia reported Nepean Hospital ICU specialist Nhi Nguyen saying a significant proportion of patients in intensive care had the Delta strain.

Data from France also suggests Delta is still causing big problems even though the vast majority of cases are Omicron.

Yes, Omicron could be terminal to Delta (a small study from South Africa suggests this may be case), but the variant proved stubborn even in highly vaccinated countries last year.

Yes, every country is different, but so far in highly vaccinated countries data suggests the sheer weight of Omicron infections send a lot of people to hospital, but a much smaller proportion to ICU, compared with Delta.

What does this mean for NZ?

If we assume Omicron is inevitable, the question is when would its arrival be optimal? It would clearly be beneficial to New Zealand to boost as many people over 18 as possible, to vaccinate children and to have a significant supply of rapid antigen testing to help limit spread.

Two doses of the Pfizer vaccine holds up well against the worst effects of Omicron. Three doses is even better and should dampen down transmission.

A nightmare scenario would be an Omicron incursion as Delta cases surged. If this happened in winter, it’d be even worse. ‘‘If we’re preparing for an Omicron outbreak, no Delta would be an advantage. You’re dealing with one outbreak rather than two,’’ Baker says.

Professor Tony Blakely makes a similar point. Eliminating Delta would be fantastic. Keeping it muzzled is vital. ‘‘The trick will be for New Zealand to really keep clamping down on Delta when/as Omicron takes hold. If at all possible, keep those contact-tracing efforts prioritised on Delta.’’

Could Delta spark up again?

Throughout the pandemic, we’ve seen younger people make up a high proportion of Covid-19 cases.

In a piece for The Conversation, epidemgiologist Professor Catherine Bennett wrote of the importance of vaccinating younger people. These people are the most mobile, they socialise a lot, they live in shared houses, they tend to have lots of close contacts. The Doherty Institute’s Professor Jodie McVernon said people aged 20 to 29 in particular were ‘‘peak spreaders’’.

Vaccination rates in the 20-to-29 age group are good overall, but not as good as the rates in the older age categories.

As Stuff has reported, it may have worked out in our favour (in the short term) at least that New Zealand vaccinated its most mobile demographic just before entering the traffic light system and accepting some virus in the community.

This brings us to the dilemma New Zealand now faces. Those ‘‘peak spreaders’’ will be the last to be boosted. Most people in their 20s were vaccinated in October and November. Their protection against infection is waning. Yes, it’s still good – two Pfizer doses are about 80 per cent effective at preventing symptomatic illness after 10 to 14 weeks, according to UK numbers. But it continues to fall off, making breakthrough infections a little more likely.

This is why right now may be our best chance to get rid of Delta.

On the flip side, boosting those in the older age groups makes sense (and is obviously unavoidable given the four-month gap). This will offer the most vulnerable better protection from infection and serious illness – which will be vital if we see Omicron case numbers comparable with those overseas.

Could we eliminate Delta then?

Wilson believes we could. There is a chance if there’s a focused effort, by ensuring active cases are placed in MIQ, there’s aggressive contact-tracing and infected people are provided with excellent and ongoing support – to, for example, ensure they don’t need to leave the house.

‘‘The system so far has stopped ongoing transmission. There’s certainly no need for suburb-level lockdowns. What they’re doing is working.’’

Baker is also optimistic. He says we pretty much have eliminated Delta in parts of New Zealand. Cases have popped up in Christchurch, for instance, and have been stamped out.

The question would be whether it’s possible to eliminate the remaining clusters all at once.

What’s more, he says, there may well have been cases missed over the Christmas period. Now people are going back to work, children will soon go back to school. Have people simply put off tests over the break?

The next few weeks will be very telling, he says.

Plank is a little more circumspect. Technically, it’s possible, he says. ‘‘But I think it’s unlikely it would happen organically if we continue on as we are. I think it would take a really concerted effort.’’

* Data reporting by Kate Newton.