Bloomfield said there would be some changes to the reporting of Covid related deaths. Video / NZ Herald
New Zealand's hidden Omicron iceberg has highlighted an urgent need to beef up our Covid-19 surveillance, as experts fear officials are "flying blind" without better data.
Amid rising case numbers and new testing processes and advice, we could only be sure that the country's "case ascertainment rate" - that's the fraction of infections recorded as known cases – was shifting over time, said Dr Dion O'Neale, of Covid Modelling Aotearoa.
"It's most likely that this is falling due to people's difficulty or reluctance to seek a test."
Hospitalisation numbers have been suggested as a useful indicator, because they weren't sensitive to swings in testing trends - but O'Neale said they were nonetheless a "dangerously lagged" one.
"Looking at hospitalisations to measure infections means that by the time we see hospitalisations reach a number where we might need to act, it is already too late to prevent additional hospitalisations from coming," he said.
"The infections that correspond to those additional hospitalisation have already occurred over the past couple of weeks."
Testing wastewater could also give a broad signal of community infection – but it couldn't tell us precisely how many people had the virus, and importantly, which groups in the population were being affected more.
Instead, O'Neale saw the "gold standard" as a large-scale programme like the Covid-19 infection survey run by the UK's Office of National Statistics (ONS), designed to directly estimate the number of infections in the population.
Drawing on a pool of 150,000 weekly samples, it offered regular snapshots of daily infection numbers, along with the percentage of Britons testing positive for Covid-19 antibodies.
"Without one, decision makers and public health officials are flying blind and modelling results become less valuable without being able to verify their underlying assumptions," O'Neale said.
Fellow modeller Professor Michael Plank agreed an ONS-style survey would be a "gold mine" of crucial information.
"You can work out from it things like how many people aren't getting tested, and you can track how many people have had the virus over a period of time, which is important because it determines the amount of immunity in the population."
While the country was already in the thick of a national wave of Covid-19, Plank said we needed such a tool as soon as possible.
New Zealand recorded another 21,000 Covid-19 cases yesterday. The total picture of infection could sit between 500,000 and one million cases. Photo / Alex Burton
"After this peak, for instance, and case numbers start coming down, it won't be clear how much of that fall in cases is real, and how much of it is due to people perhaps perceiving the threat has passed, meaning they're less likely to get tested," he said.
"Having a representative sample would answer that. Of course, new variants are expected to come along as well, and it would give us a really useful surveillance tool to track them."
In an analysis this week, a team of health researchers said having an ongoing survey could help track post-acute, long-term symptoms among Kiwi children, and highlight likely inequities around incidence and healthcare access.
They pointed out how a recent ONS analysis showed how, between March 2020 and in November and December last year, around 1 per cent of all primary-aged kids and 2.7 per cent of all secondary-school aged children met a criteria for lingering "Long Covid".
A Ministry of Health spokesperson said the ministry did plan to undertake prevalence surveys to identify the number of Kiwis who had Covid-19 at a specific point in time, as well as serological surveys to better understand the level of immunity in the population.
The spokesperson said these surveys would include testing "a statistically appropriate" sample of the population, to estimate true prevalence.
But it wasn't yet clear whether it would run longitudinally, like the UK's.
"Design work is underway and we expect to have something in place over the coming months."
Otago University epidemiologist Professor Nick Wilson said a prevalence survey should be just one part of a better Covid-19 surveillance system.
While the Government just updated New Zealand's official strategy, Wilson saw scope for better data collection from a range of sources like from hospital emergency departments, wastewater testing, and school absenteeism.
"This pandemic has cost the country billions of dollars, so it would be worth spending millions on a state-of-the-art system," Otago University epidemiologist Dr Nick Wilson says. Photo / Supplied
All of this information could be fed into a dashboard like EpiSurv, our main notifiable disease database.
"This pandemic has cost the country billions of dollars, so it would be worth spending millions on a state-of-the-art system," Wilson said.
In the meantime, researchers urged Kiwis to keep reporting positive rapid antigen test results, and filling out contact tracing forms that followed.
Covid-19 modeller Dr Emily Harvey said this was "incredibly important" as it was the only way agencies would know about patients' situations, and what support they might need.
"It also helps to flag anyone with high-risk health needs where more regular health check-ins would be prioritised," she said.
Reporting negative tests through time - especially in close or household contacts, or recent border arrivals, would also be valuable for informing guidelines around the duration of isolation, or testing frequency.
"We need this data to be able to answer questions like 'what proportion of household contacts will go on to get infected?' and 'for household contacts that get infected, how soon would we expect to detect the infections using RATs?'."
