Epidemiologist Sir David Skegg has questioned the Government's definition of community transmission, saying without knowing exactly how many people have caught COVID-19 within the country it will be difficult to know when we can leave lockdown.
Sir David addressed the Epidemic Response Committee on Tuesday.
"It's easy to be numbed by the repetition of statistics," he said, referring to the staggering amount of cases worldwide and the mounting death toll.
As the situation both in New Zealand and abroad changes every day, Sir David stressed the importance of constantly updating policy as new information about the virus arises.
"In a pandemic of this kind, decisions have to be made quickly on the basis of imperfect evidence. New information is coming to hand every day so we all have to be willing to modify our opinions and policies," he said.
"Governments, as well as individuals, must avoid sticking to previous positions when new evidence indicates a need for change."
One area where policy needed to be updated, hinted Sir David, was in how the Ministry of Health defined community transmission.
"Now if I was infected at a wedding reception, I would call that community transmission. The Ministry uses a much narrower definition.
"I'm not criticising this because internationally that term is sometimes used only when the source of an infection is unknown - but it's important to recognise the different usage," he said.
He said that because the virus did not originate in New Zealand, every single case would be linked to overseas travel - and hence would not be considered a case of community transmission - if we could uncover all the chains of transmission.
But the reality of the current definition makes it difficult to accurately plot the spread of COVID-19 within the country, he said.
"What we need is to see two curves plotted: the cases who arrive from overseas and the people who have been infected here.
“Regrettably, the data provided from the Ministry do not make this possible."
Sir David expressed cautious optimism in the fact that numbers of new cases had appeared to level off over recent days.
"That gives us all hope. But the hope must be tempered by the fact there are two major components to our epidemic."
The first component was the cases originating overseas, while the second component was the internal spread of the virus.
In speaking to the committee last week, Sir David criticised the Government's apparent lack of a concrete plan to eliminate COVID-19 here, saying it seemed to rely solely on the lockdown as a solution.
"A lockdown on its own is not enough. It's like pressing the pause button on your device," he said at the time.
But on Tuesday, he said he was "delighted" that the Government had now confirmed its goal was to eliminate the virus.
"We need absolute clarity about the goal and how we're going to achieve it," he said, adding that elimination did not necessarily mean stamping out each and every case of the virus here.
"Small outbreaks of COVID-19 may still occur, but these can be managed by rapid identification, contact tracing and isolation."
He said that if it appeared that the country was on the path to elimination, lockdown measures could be relaxed.
"Elimination will be the best outcome for social life, jobs and the economy, as well as for health. If we can show that we are on the path to elimination we can move out of the lockdown quickly. Unlike so many other countries we can avoid lockdowns that last many months or need to be repeated continually."
To successfully eliminate the virus, there were four key factors, he said: having an initial comprehensive lockdown, preventing the spread of COVID-19 from Kiwis returning to the country, increasing testing and ensuring rapid contact tracing.
On Monday, Prime Minister Jacinda Ardern admitted that the Government needed a better understanding of community transmission in order to rule out the risk of wider unseen transmission, especially in areas showing low case numbers.