An epidemiologist suspects Australia's encouraging Covid-19 figures may not be giving the full picture of infection in the country.

As at yesterday, New Zealand had 1239 confirmed and probable cases of the virus – about 0.02 per cent of the population – with 317 recovered.

That was roughly the same proportion in Australia with its 6103 cases, around half of which had recovered.

Both countries have also been seeing positive test rates of around 2 per cent - a comparatively good proportion, globally.

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While some commentators across the Tasman have argued Australia has been able to achieve similar results to New Zealand without opting for a complete, nationwide lockdown, Professor Tony Blakely questioned whether the data was telling the whole story.

"If you look at the data, per capital daily case rates of Australia are the same as New Zealand's even though we're not going for elimination – that makes you scratch your head," said Blakely, an honorary Otago University academic based at the University of Melbourne.

"Dig a little bit deeper and you'll see that we've got considerably higher hospitalisation rates."

As at yesterday, 263 of Australia's current cases had been admitted to hospital, with 87 in intensive care.

On the other side of the Tasman, there were 14 current cases in hospital, with four in intensive care.

"What I take from that is New Zealand is doing a better job testing and finding those people out there who are asymptomatic or have very mild disease, and we must be missing them in Australia," he said.

"Dig a little bit deeper and you'll see that we've got considerably higher hospitalisation rates," University of Melbourne epidemiologist Professor Tony Blakely says. Photo / Supplied

"So even though the daily rates in Australia per capita are much the same compared with New Zealand, you just look at the hospitalisation rates in New Zealand and they're much lower.

"I think we must be missing quite a lot of mild disease. It would suggest to me that there is actually be a bigger rump – or a bigger disease burden – in Australia per capita than in New Zealand, which makes sense given that New Zealand is going for all-out elimination."

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Australia has responded to the crisis with a raft of measures, such as closing businesses and community centres, and banning people from travelling overseas.

"You could say we're in near lockdown – we can still go to Bunnings or go exercise in the next neighbourhood."

Blakely thought Australia had done well in squashing its curve – or suppressing the virus – but felt the country had probably missed the chance to pursue elimination in the aggressive way its neighbour had.

He pointed to government material released on Tuesday, which contained no scenarios about how such a strategy would play out.

"I found that annoying and quite disappointing that we didn't have those estimates. I've been contacted by people who are really looking hard at whether Australia could go for elimination and I think it's probably unlikely."

But he added that, even if it did, there existed the risk of the virus bouncing back.

"It's out there globally and it is going to come back at some point in time. We don't know whether a vaccine can be developed for it – we are hoping it can – but then the vaccine might not have the perfect ability to make people immune."

One of the upsides to achieving elimination – and provided New Zealand could do the same – was the prospect of re-opening the borders between the countries.

"We could still have people moving across the ditch, even though we'd be collectively isolated from the rest of the world."

In any case, he thought Australia had squashed its curve down much lower than he'd expected.

"If you look at data just for New South Wales, for example, and look at local cases, they're going down – they should really be going up.

A deserted Sydney Opera House, pictured on March 20. Photo / Matthew Abbott / The New York Times
A deserted Sydney Opera House, pictured on March 20. Photo / Matthew Abbott / The New York Times

"But I'd turn to Singapore, which did a really good job of bringing the virus under control – but now their rates are just moving into a trend of slowly going up, or doubling every 10 days, rather than four.

"So it's not taking off like a bushfire, more just simmering and perhaps then coming on like an epidemic. It may be that New South Wales' rates kick up in a week or so, once people get sick of social isolation and all the rest of it, but essentially, at the moment Australia is doing pretty damn well."

Epidemiologists had been predicting a worst-case scenario of up to 130,000 deaths for the country, if it had attempted to "flatten" the curve through mitigation, rather than suppressing it.

Blakely said that, by protecting the elderly and achieving better treatment – potentially with old retroviral drugs – the death rate could be cut to 30,000, which was about 10,000 more than died from tobacco-related causes.

Whatever happened, he said Australia's leaders would need to pick its course of action, and fast.

"Do we keep trying to suppress the hell out of it? We need to make the decision about what we do for the next 18 months. Think, and then commit to a plan. New Zealand, at least, has got one and is giving it a crack."

There was also worry about the level of transparency in Australia's decision-making, he said.

"Interestingly enough, Australia completed its most recent pandemic plan last year, and the first principle was openness and transparency. Many of us here are concerned that transparency is not being abided by.

"One senior reporter here noted that New Zealand makes its Cabinet papers available to the public scrutiny after six weeks. Over here, it takes 30 years."

Covid19.govt.nz: The Government's official Covid-19 advisory website