A second Omicron wave could peak within weeks, perhaps reaching past 15,000 daily cases. Photo / Michael Craig
New Zealand will soon be in the thick of another Omicron wave – but it won't be the same as last time. Science reporter Jamie Morton looks at three key differences.
When New Zealand first confronted Omicron in late February, our collective immunity was almost exclusively built on vaccination.
As we soon found, even boosting two thirds of the eligible population couldn't stop mass community transmission – and perhaps 60 per cent of Kiwis became infected.
It did, however, spare a large number of people from severe sickness: boosting remains close to 90 per cent effective against hospitalisation two to five weeks after the shot.
The difference now is that much of the vaccination-given immunity will have waned.
If you're among the 2.6 million people boosted more than three months ago, your vaccine-derived protection might have fallen substantially.
Over just three to six months, booster effectiveness against symptomatic infection with Omicron can drop to about 40 to 50 per cent, although protection against hospitalisation still stays relatively high, at 75 to 85 per cent.
Fairly consistent growth in cases still, back to level we were at 3 months ago but doubling every 2-3 weeks. pic.twitter.com/RcmHiKRgy0
— David Welch (@phydyn) July 9, 2022
University of Auckland immunologist Associate Professor Nikki Moreland said it was difficult to say just what New Zealand's current level of immunity looked like now.
"Even with antibody waning, there will still be good levels of immune memory from the vaccine to help protect people from the very worst outcomes," she said.
"And if they've been infected, they'd have hybrid immunity too."
This was something studies show can greatly reduce the risk of severe outcomes from reinfection.
One major Qatar study, released before peer review last week, indicated previous infection with Omicron afforded more than 97 per cent protection against severe, critical, or fatal reinfection.
As it's proving around the world, the BA.5 subvariant happens to be a master at evading immunity – and the latest modelling has indicated that up to 45 per cent of cases in this wave could be reinfections.
Some studies have also indicated BA.4 and BA.5 may be four times more resistant to antibodies from vaccines than BA.2 - but still, a second booster remains the best defence for at-risk people eligible for one.
"People over 50 are at the most risk of severe disease – and they're the ones eligible to get a fourth dose," said Dr Dion O'Neale, of Covid Modelling Aotearoa.
"If this group goes out and gets their boosters, they could be coming into this wave relatively well protected against severe disease."
The exponential rise of BA.5 - which may have already overtaken BA.2 as our dominant form of Covid-19 – has left experts with no doubt another potentially large peak is now just weeks away.
The latest wastewater surveillance showed 19 of 20 sites were positive for BA.5, which has recently been doubling in recorded incidence roughly every six days.
Under relaxed border settings, BA.5 has been liberally seeded into our communities at a rate of one overseas-linked case a day - adding to the current growth rate and giving this wave a region-by-region uniformity not seen last time.
Last week, O'Neale's fellow modeller Professor Michael Plank said this surge might well top out with daily cases stretching past 15,000 – and perhaps even close to 20,000, or not far off March's peak of almost 24,000.
There was still uncertainty in the modelling around whether the peak would be lower or higher this time.
"There are certainly a lot of countries where BA.5 waves had actually driven cases higher than what they saw with BA.1 and BA.2," O'Neale said.
Every week I help to coordinate ESR’s genomics reporting with an amazing group of scientists. There is now a public dashboard of this report: https://t.co/ZF4js0L8vl -a weekly snapshot of the work we do to monitor this ‘tricky virus’ which is constantly changing the playing field pic.twitter.com/7SgtRH22TO
— Michael Bunce (@BunceDNA) July 7, 2022
Not only was BA.5 better at evading immunity than its predecessor, it also appeared to be much more transmissible – partly because of mutations in its spike protein thought to help it better latch on to human cells.
Still, O'Neale said its knack of dodging immunity was its real weapon.
"If we saw either BA.2 or BA.5 spread in a population that didn't have any immunity at all, in terms of the severity of health outcomes, the picture would actually look fairly similar," O'Neale said.
"That main thing BA.5 is doing is avoiding a lot of that immunity people got with prior infection."
Omicron hit our more mobile and socially connected young first: 91 per cent of cases in the first wave were under 60.
Over time, however, that concentration of cases has shifted to older Kiwis. Those aged over 70 are about six times more at risk of hospitalisation than young adults.
Of a total 720 people whose deaths have been formally attributed to Covid-19, all but 42 were over 60.
"Teens and people younger are now actually a smaller fraction of total cases compared with what they were in May, while the proportion of total cases in people aged over 60 has gone up by about a third," O'Neale said.
"These are often people who are being infected for the first time."
Because of that shift, modellers warn the volume of hospitalisations linked to this wave may be higher this time, even if the actual case count turned out to be lower.
And the tail of hospitalisations – it took nearly three months for daily hospital cases in the first wave to fall from a high of more than 1000 to a baseline of several hundred – might also stretch out longer.
Unfortunately, another spike in hospitalisations also meant another bump in virus-linked deaths, of which there have already been more than 1500 since Omicron's arrival.
ESR's bioinformatics and genomics lead Dr Joep de Ligt agreed a demographic shift was contributing to more people needing hospital care, but so too was the sheer case numbers that each Omicron wave caused.
"Part of that is more people are getting infected again and, therefore, more people are ending up in hospital."
Of course, another wave of cases also exposed more people to the risk of Long Covid, particularly if they were catching the virus a second time.
One recent US study showed that, compared to those with a first infection, reinfected people had at least one condition linked with Long Covid that still lingered on even six months afterwards.
De Ligt said how we all responded to the threat – and that meant getting vaccinated, wearing masks and staying home when sick – would matter immensely over coming weeks.
"While BA.2 looks to be at the end of its journey, BA.5 has a fresh playing field in front of it – and unless we put something in its way, it could well follow a similar trajectory to BA.2."
They allege the Crown ignored Treaty obligations by not engaging with them.