24 Apr 2020

'The possibility of reinvasion of the disease is very strong' - Shaun Hendy

From Checkpoint, 5:16 pm on 24 April 2020

One of New Zealand's leading Covid-19 researchers believes it is possible that our borders with Australia could be reopened in coming months, if both countries achieve elimination of the Covid-19 virus.

Over the past six days the number of new Covid-19 cases in New Zealand has slowed to fewer than 10. That is down from peaks in the high 80s at the beginning of level 4 lockdown. 

Friday's new confirmed or probable cases were five, bringing New Zealand's total to 1456.  

Auckland University Professor Shaun Hendy led the Te Punaha Matatini research team that modelled the worst case scenario for the virus. 

He told Checkpoint the first step is to get the number of infections down to just a handful for the next couple of months, with no undetected spread.

Professor Hendy said reopening the border will have to be phased in slowly.

"Perhaps having family members reconnected, who have been separated across the Tasman by the lockdowns. And then maybe eventually looking to more widespread travel, but it is something we want to be cautious about. But certainly it's a possibility."

He told Checkpoint both countries would have guard against a second wave of Covid-19, as Singapore has experienced.

"It looked like [Singapore] was tracking very well, it was one of the early countries that we followed and were looking to. They've had a second wave and come back unfortunately.

"There's not a lot of immunity to this disease, even with the cases we've had. 

"So the possibility of reinvasion of the disease is very strong."

If someone in New Zealand catches Covid-19 currently, the number of people they will pass it on to on average is less than 0.5, Professor Hendy said. 

"It's telling you that you're slowing the spread of the disease down. And eventually, if you keep that number that low, for another few weeks, then we'll be very close to elimination." 

The definition of "elimination" is debated among epidemiologists, but Professor Hendy said he would be comfortable saying elimination is achieved when there are no new cases for a number of days. 

"We don't know how well level three is going to work. One of the things we were concerned about was Anzac weekend. If we'd come off level [four], going into the Anzac weekend, and everybody just headed out to see their friends, to the beach, then that could have reignited the spread of the disease. 

"So we've got to really wait and see for a little while - a week to 10 days into level three before we start to get an idea of how well level three is working. 

"Then we'll be able to make a call about when elimination might be likely."

How are some of New Zealand's biggest clusters still growing through lockdown? 

"Part of this has to do with contact tracing and testing," Professor Hendy told Checkpoint. 

"People are still working through and identifying some of these cases. The disease takes a while to incubate and then symptoms come on a little bit later. So it can take a while to close the envelope around those clusters, and I think that's what we're seeing going on.

"There are some clusters that have taken a long time for them to track down, and of course, as that bubble expands out, as you go out further and further into the cluster, you've got to talk to more and more people. 

"So it can take a long time to really draw a circle around the cluster.

"One of the reasons we're seeing quite large clusters is because we've brought the numbers down and it's given time for our contact tracers to actually go out and do that.

"In other countries around the world that their contact tracing has just been overwhelmed by the number of cases."

If New Zealand's Covid-19 new cases start getting back in to double digits in the next two weeks, that would signal a need to return to level 4 lockdown, Professor Hendy said. 

"If we started to see double digits of community transmission cases we couldn't tie to one another, then we'd start to be quite alarmed. And I think we'd have to restart the conversation about level 4."

Is two weeks at level 3 long enough to know if we're improving or not? 

"We're looking at that at the moment. It will be pretty hard for us to tell, I think, unless level 3 is really bad… and we see a quick resurgence, then we'll probably be able to call it by the end.

"If level 3 is middling or quite good, we may be still a little bit uncertain. But that's sort of a sign in itself, if we're still a little bit uncertain as to exactly how effective level 3 is, then we can perhaps be confident about shifting to level 2."