Later, in November, deputy director of health Dr Andrew Old told RNZ the survey had been delayed until 2023, with a second phase not due to start until July.
Old put the delays down to “Covid-19 and winter illness surge on our health sector, as well as the resetting of roles and responsibilities, governance, priorities and budgets prompted by the health sector reforms”.
In March, the ministry told the Herald that it was instead looking at a “changed way forward”, with an update expected in April.
At that time, it was understood there were proposals to survey a demographic sub-set, rather than a large sample of the wider population.
More than a week after the Herald inquired again last Tuesday, the ministry today responded with a statement that it had agreed Covid-19 prevalence surveys “should not advance in their proposed current format”.
A spokesperson said New Zealand had “passed the emergency stage” of its Covid-19 response, with the virus endemic in our communities.
“The results of any Covid-19-focused prevalence survey would be unlikely to meaningfully alter any current public health response as there are only two pandemic-related mandates still in place.”
But the ministry accepted that it took “longer than expected” to reach this conclusion, citing challenges of a “multi-stakeholder, complex” project developed during the health reforms.
“Prevalence surveys are expected to be a key tool in any future effective population and public health knowledge surveillance system,” the spokesperson said.
“Any future survey design will benefit from lessons learned during the Covid-19 prevalence surveys project and, where appropriate, will leverage technologies and ways of working established during the pandemic.”
Last month, Covid-19 modeller Dr Dion O’Neale said prevalence surveys would be “incredibly useful” for monitoring New Zealand’s true immunity landscape.
Without one, it was difficult to assess our current case ascertainment rate (CAR), which is the proportion of Covid-19 cases that were being picked up or reported at a given time, out of the total infections occurring in the population.
As at late 2022, the CAR was thought to be just 30 per cent - with a higher rate in adults but a lower one in children – meaning about two-thirds of cases are probably going undetected.
Fellow modeller Professor Michael Plank however acknowledged the public health threat posed by Covid-19 had changed “enormously” over the past 12 months.
“Although from a scientific point of view, getting representative data on the true number of Covid infections would be gold dust, it may seem from a public health point of view that this kind of data is not so essential,” he told the Herald in April.
“We are no longer in the emergency phase of the pandemic where we need to react strongly to very rapidly changing situations.”
Still, he added there were areas where this kind of data could provide significant public health benefits.
“If a new variant arrives that causes more severe disease, it will be very difficult to detect without knowing the true number of infections,” he said.
“And having representative data on infections could help build a more accurate picture of how much vaccines and boosters reduce transmission, on top of the known benefits in reducing severe disease.
“Designing an infection survey where samples can be tested for multiple viruses and that ensures the needs of at-risk communities are met would be good ways to ensure it delivers good value for money.”
Otago University epidemiologist Professor Michael Baker earlier told the Herald that last year would have been the optimal time for a Covid-focused survey.
“Now we need robust surveillance of serious respiratory infections, including Covid-19, influenza, and RSV.
Baker saw it as “critically important” to identify the purpose of the surveillance system and the questions that we need to answer on an ongoing basis.
“Such surveillance is vital public health infrastructure and also needs to be there for future pandemics, which are most likely to be respiratory viruses.”
He suggested the simplest and most sustainable option could be to establish a series of respiratory disease sentinel surveillance sites.
