Health experts are tracking a rise in flu cases at the same time that newly-arrived Covid-19 subvariants look set to begin a second Omicron wave. Photo / Getty Images
Health experts are tracking a rise in flu cases at the same time that newly-arrived Covid-19 subvariants look set to begin a second Omicron wave. Photo / Getty Images
Health experts are tracking a rise in flu cases at the same time that newly-arrived Covid-19 subvariants look set to begin a second Omicron wave – spelling an especially tough winter for hospitals. Science reporter Jamie Morton explains.
What's worrying health experts?
In a word: "twindemic".
That's Covid-19 spreading through our communities alongside influenza and other resurgent seasonal nasties that have been locked out of New Zealand for more than two years.
There are early indications these viruses might align to cause a mass of infections in our communities this winter, at a time hospitals are already under heavy strain.
When New Zealand moved to the orange traffic light setting in mid-April, the rolling average of daily cases was sitting at around 10,000.
As at today, that average was just under 5000, which was higher than modelling had earlier projected, but still much lower than the early-March daily peak of close to 24,000 cases.
University of Auckland computational biologist Dr David Welch said older people had generally been more cautious and able to protect themselves throughout the pandemic.
"But now that it's really a widespread thing, with a lack of public health interventions, it's pretty hard for someone to shield themselves."
Why are we talking about a second Omicron wave already?
Perhaps 60 per cent of Kiwis have now had Covid-19: and those who've caught the virus over the last few months have likely met Omicron's "second generation" subvariant, BA.2.
Right now, BA.2 is still responsible for about 95 per cent of sequenced local cases, but scientists are watching three new subvariants – BA.2.12.1, BA.4 and BA.5 - beginning to take off.
A quick overview of the new variants taking hold in Ao/NZ. Lots of people have been seeing the public data on cases/hospitalisations, not so much the ESR variant data at https://t.co/4cAyRhn2oS maintained by @TheAtavism 1/ pic.twitter.com/ZARuTJ7goT
Covid-19 modellers hadn't been expecting our second wave until around late winter or early spring – but overseas experience and data trends suggest we're in for another surge much sooner.
"If you look at ESR data on the frequency of the different variants, you can see quite clearly that they are on the increase," said Professor Michael Plank, of Covid-19 Modelling Aotearoa.
"It's not entirely clear which one is going to win out... but it looks at least like one of those variants is likely to take over – and that's likely to happen at some point in the next month or so."
Put together, the three variants' share of total cases has been roughly doubling each week.
"If we plug that sort of growth rate into the model, we can see that does trigger a significant wave of cases: potentially not as big as the March peak, but possibly not far off."
Just how that translated into hospitalisations and deaths – daily rates of those have been averaging 371 and six respectively – was harder to tell, as there still wasn't good data on the subvariants' severity.
"But if we see an increase in cases, that will naturally flow on into hospitalisations," Plank said.
Welch agreed that, with slightly better immune evasion properties, and possibly also a transmission advantage, the new subvariants would quickly reverse the declining case trend.
"We'll see cases rising... and basically the start of a new wave."
Will I get Covid-19 again?
Recent modelling by Plank and colleagues included one scenario where nearly half of those cases in the second peak were people who'd already had Omicron.
But that work was focused on BA.2, and it wasn't clear how the new subvariants would change the numbers.
For many hit in the first wave, it's now been three months – the oft-cited measure of the "immunity window" - since they'd had Covid-19 anyway.
Epidemiologists predict those more social and mobile younger Kiwis, who were at the front of the first wave, will be among the first infected in the second.
"Most people also would have had their booster shot more than three months ago too," Geoghegan added.
Given the Ministry of Health didn't yet collect and publish data on reinfections, it was difficult to know precisely how many were occurring – but Geoghegan noted that cases were under-reported regardless.
"Generally, we know that reinfection is going to happen – and weakened immunity helps with that."
What about our reopened borders?
The Government last week removed a requirement for people to self-test before travelling to New Zealand: an average 80 infections are being detected in arriving visitors each day.
At the end of July, borders will finally reopen to all travellers, bringing in a deluge of international tourists.
Some experts have raised concern that, with no pre-flight measures in place, this influx could quickly and more easily seed new variants here, while putting our already patchy surveillance under further strain.
In the particular case of a second wave and the already-establishing BA.2.12.1, BA.4 and BA.5, that point might be moot.
Re-opened borders are expected to seed more influenza cases and bring new variants into New Zealand. Photo / Brett Phibbs
But Geoghegan said our reopened borders would mean New Zealand no longer had a "head-start" at preparing for new variants before they arrived here.
"We'll basically get them at the same time everyone else does."
This is where reopened borders will have an especially big impact.
The flu traditionally infects around one in four Kiwis each year, while causing an estimated 500 deaths - making it hitherto our single worst infectious disease killer.
It might seem like a lifetime ago now, but 2019 was the last time New Zealand experienced a flu season.
When Covid-19 arrived early the next year, the unprecedented steps we took to block it also brought the hammer down on influenza.
With closed borders stopping the main way the virus is seeded here - through international visitors - and a national lockdown stamping out what was still circulating, flu rates swiftly plummeted by an incredible 99 per cent in 2020.
According to the latest Flu Tracking surveillance, Covid-19 was still currently responsible for nearly half of flu-like cases in the country, while flu accounted for fewer than 1 per cent.
But, in Australia, cases of the flu have been spiking, and hospitals have been bracing for the same surge here.
"It's inevitable that we'll have reintroduction of flu and we're probably already seeing more cases now than pre-pandemic because of the fact we have weakened immunity to it and haven't seen it for a couple of years," Geoghegan said.
What else is coming back?
We're also likely to see the swift return of a host of other viruses: including human metapneumovirus (HMPV), enterovirus, adenovirus, rhinovirus (which causes the common cold), the highly-contagious measles, and respiratory syncytial virus (RSV), which drove an epidemic last year.
Because respiratory viruses like flu traditionally peaked over the winter months, a mid-season reopening of borders wasn't ideal – and nor was the potential alignment with another Omicron wave.
"Someone also asked me whether you can be infected with both flu and Covid at the same time: of course, you can," Geoghegan said.
"But I'd add that the same precautions we have against Covid-19 – that's wearing masks and isolating if you or your household gets it – also reduces your risk against flu.
"Ultimately, though, all of this is going to be putting more pressure on healthcare system, and RSV will probably be added to the mix soon too."
She said people could ease that burden by getting their flu and Covid-19 vaccinations, staying masked up, and keeping themselves at home if sick.
