Why it’s so important to go hard and go early

Analysis: Our testing regime for Covid-19 will often be several days or weeks behind, underscoring the need to act as if we're two weeks ahead of where we are, Marc Daalder reports

On March 25, the day New Zealand moved into Level 4 lockdown, the official Covid-19 case tally was 189 confirmed cases and 16 probable cases. There were actually 552 cases that would be confirmed and 60 cases that would be considered probable in New Zealand that day.

As the Government scrambles to contain an outbreak of unknown scale and spread in Auckland, it has chosen to take what Jacinda Ardern has described as a "precautionary approach". With little information about the four confirmed cases identified in an Auckland family today and no known link to the border, overseas travel or managed isolation facilities, the Government has announced Auckland will move to Level 3 and the rest of the country will move to Level 2.

This strategy is predicated on what worked to eliminate Covid-19 in New Zealand originally and on Director-General of Health Ashley Bloomfield's long-time refrain with regards to the virus: that we should act now as if we are where we could be in two weeks.

The above statistics vindicate that strategy. Case data from the Ministry of Health shows there are 462 Covid-19 cases linked to overseas travel that entered the country on or before March 25. While many of these people might not have been symptomatic at the time, they were still incubating the virus and risked spreading it to others asymptomatically or at a later date.

The decision to enter lockdown meant that these people would not be able to unwittingly spread Covid-19 in their communities.

Some of the delay in identifying the hundreds of cases in New Zealand in late March can be laid at the feet of a testing system ill-equipped to handle a surge in demand. This time around, the Government has promised to launch a mass testing effort in Auckland, swabbing tens of thousands of people including everyone with symptoms and everyone involved in border or managed isolation operations.

Nonetheless, the mere fact that SARS-CoV-2, the virus that causes the Covid-19 disease, has an incubation period of five days before showing symptoms on average means even the world's best testing system would not identify all active or soon-to-be active cases. That a significant but unknown chunk of Covid-19 cases never experience any symptoms at all further entrenches this reality.

The only way to be confident that all or most cases are contained is through contact tracing. But the fact that these cases have cropped up without an apparent source means there is a missing link between them and the border.

In the absence of a clear link between the new cases in the community and a plausible source of infection - the border, overseas travel or the managed isolation system - the scale and spread of the outbreak cannot be assessed. That leaves few viable options going forward beyond a longer-term effort to suppress the virus, unless that missing link is identified in the coming days.

On June 12, the Australian state of Victoria reported eight new cases, just two of which were locally-acquired or still under investigation. Two weeks later, there were 40 new cases, only one of which was from overseas or interstate travel. Two weeks after that, there were 149 new cases in Victoria, all of which were locally-acquired.

On Tuesday, for the second day in a row, Victoria reported a record 19 deaths from Covid-19. Nearly 250 people have been killed by the disease in Victoria since the pandemic began.

We are acting as if we are now where we could be in two weeks. Our four cases now may just be the tip of the iceberg - and we may not know that until it is too late.

For Victoria, that meant 40 new cases a day, up from eight daily cases two weeks earlier. In a striking coincidence, in New Zealand on March 18, there were 40 new cases in the country - even though we only identified eight new cases that day. 

Without solid information about the source of our four new cases, the best option available to us is to go hard and to go early. It is by no means a foolproof approach, but it is the best we've got.

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