Covid-19

New modelling shows scale of Covid-19 threat

The Government has released the modelling it used to inform its decision to lock down the country, and the numbers paint a stark picture of the threat Covid-19 poses, Marc Daalder reports

Last week, Jacinda Ardern said if she didn't take the unprecedented step of locking down the entire country for a minimum of four weeks, "tens of thousands of New Zealanders will die".

The figures she based this assertion on have now been publicly released and they show the scale of the threat Covid-19 poses to New Zealand.

The Government relied on seven different models to inform its decision-making, two of which have already been released. One is an Imperial College London paper that estimated millions of Americans and hundreds of thousands of Brits would die without severe suppression measures like a lockdown. The paper altered policy in the United Kingdom, United States and, as Newsroom reported, New Zealand as well.

Researchers at Te Pūnaha Matatini, the University's data-focused Centre of Research Excellence, then applied the Imperial College modelling to New Zealand and found 80,000 Kiwis would have died if the Government had taken no action against Covid-19.

Early reports warn of greatest danger

The new projections released today are similarly dire. A draft report commissioned by the Ministry of Health in late February found that 72 percent of the population could contract the virus if no action was taken. Just over half of these patients - 1.85 million - would be symptomatic.

Over the period the virus spread in New Zealand, it would hospitalise 370,000 people. The peak day would see 10,000 new patients requiring hospitalisation and up to 2350 new patients needing intensive care - four times the peak intensive care capacity of New Zealand. Between 14,000 and 37,000 people would die.

The modellers only estimated the Government would be able to impose infection control - policy interventions to reduce the spread of the virus - of 50 percent, but noted further control would be possible via border closures and a lockdown. Under the 50 percent control scenario, deaths would be lowered to 10,200 from 27,300.

In modelling sent to the Ministry of Health on March 16, two of the same modellers revised their estimates somewhat lower. Assuming a reproduction rate or R0 of two - that every one person with the virus passes it on to two others - the researchers found uncontrolled spread of Covid-19 would hospitalise 124,000 Kiwis - 19,000 of whom would need intensive care treatment - and kill nearly 11,000.

The research found that intensive care capacity would still be overwhelmed. "To put the demand on ICU services into context, we note that the Wellington ICU currently treats about 1700 patients each year. If it is serving around 10 percent of the NZ population, [...] it may have to cope with 1.1 times its normal annual demand from Covid-19 cases alone, but all in the space of a few months," the researchers wrote.

If lockdown fails

A March 23 report to the Ministry of Health ran the numbers on what would happen if the lockdown and subsequent actions failed to eradicate the virus. It used a reproduction rate of 2.5, which is what modellers have largely used after observing a similar rate in China. However, the Imperial College London researchers have said that an R0 of three more accurately describes the spread of the virus in Europe.

Using the 2.5 reproduction figure and assuming a 50 percent reduction in physical contact for nine months, the modellers found there would be 2.22 million symptomatic cases for that period and the three months thereafter. More than 8500 people would die.

More than 22,000 people would need hospitalisation and 5540 would need intensive care. On the peak day in terms of demand, there would be 3750 people in hospital and 937 requiring intensive care. Less than a month after lifting the social distancing restrictions, ICU capacity would be overwhelmed.

If the reproduction rate was instead 3.5, the modellers found the same restrictions would lead to 2.6 million symptomatic cases, 26,200 requiring hospitalisation, 6550 needing ICU care and 11,800 dead.

In the absolute worst case scenario, if New Zealand was unable to eradicate the virus, modellers found dire results in an update to the March 23 paper on March 24.

"A total of 3.32 million New Zealanders would be expected to get symptomatic illness; 146,000 would be sick enough to require hospital admission; 36,600 would be sick enough to require critical care (in an ICU); and 27,600 would be expected to die," researchers wrote.

What it means

However, these are worst case scenario outcomes predicated on the possibility that the lockdown doesn't work in eliminating community transmission in New Zealand and reducing the number of other cases to near zero.

None of the modelling bases itself off the newest reproduction rate of three from the Imperial College London, making it difficult to tell exactly how accurate the figures are. Nonetheless, the scale of the threat Covid-19 poses without sufficient action is evident. In all results, more than 10,000 New Zealanders would be killed if the country took no action.

Even "mitigation" strategies, which seek to increase social distancing while keeping society functioning and allowing schools and workplaces to remain open, would barely put a dent in the death toll. With an R0 of 2.5 but social distancing measures only 25 percent effective, the March 23 paper found deaths would jump to 12,700 - nearly 50 percent more than under the 50 percent social distancing scenario.

New Zealand's best shot is suppression strategies, as the Imperial College London paper originally found. With the lockdown now in place, combined with more effective and widespread testing than is currently operating and speedy tracing of contacts, the outbreak in New Zealand can be brought under control. This is the "containment" phase.

What comes next is eradication - bringing the number of active cases in New Zealand down to zero or near zero. We have the advantage of being an island nation with effectively closed borders. If community transmission is halted, the only way for new cases to come in are with returning New Zealanders, who are being quarantined if symptomatic, or otherwise made to self-isolate for 14 days.

The scenarios outlined above, in which Covid-19 sweeps through communities and kills thousands, can be best avoided through the lockdown measures currently in place - but they require buy-in and cooperation in order to actually work.

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