Covid-19 Chasing down an outbreak Feature image

ScienceAugust 20, 2021

Siouxsie Wiles & Toby Morris: The hunt for the missing link in NZ’s delta outbreak

Covid-19 Chasing down an outbreak Feature image

The good news: we’re closing in on the missing link. The bad news: there’s a real chance of superspreading events. Siouxsie and Toby lay it all out.

As NZ confronts its first outbreak of the delta variant, we’ve made it our mission to provide timely, clear and sensationalism-free coverage. We can only do that work thanks to Spinoff Member contributions. Join us here.

While our first community delta cluster continues to grow, yesterday brought some really good news. Whole genome sequencing has shown the cases are a close match to someone who recently returned from Sydney, which has been in the grip of a delta outbreak since mid-June. 

Not only is New Zealand’s cluster now linked to the border, but that information means we can start to get a better handle on how long delta might have been present in the community. The person arrived from Sydney on a red zone flight on August 7. That’s 10 days before the Devonport man we know as case A tested positive for Covid-19. The Sydney returnee went straight into managed isolation at the Crowne Plaza hotel in Auckland. They returned a positive PCR test on August 9 and were transferred to the Jet Park quarantine facility that same day.

As of last night, how the delta virus transmitted from our Sydney returnee to case A remained a mystery. But it’s one that we hope contact tracing, genomic sequencing, and wastewater testing will solve. On the basis of when their symptoms started, Case A was likely infectious from August 12. That’s just five days after our returnee arrived and three days after they were transferred to Jet Park. Given people incubate the virus for a few days before they become infectious that suggests we’re looking at just one or two missing links in the transmission chain that led to case A. Of course, some of those missing links might be cases we already know about, like case A’s workmate and the workmates flatmates.

But another big question remains. How many other transmission chains did the Sydney returnee and the missing links trigger? 

Given how much more infectious the delta variant is, and the number and types of locations of interest, we could have had quite a few superspreading events happen in the last 10 days. That means we should definitely be prepared for case numbers to rise in the coming days.

But it also means that everyone in New Zealand should be keeping an eye on the Ministry of Health’s locations of interest list. (The Spinoff has plotted the locations of interest on an interactive map here.) Please come forward if you’ve been at one of them at the times listed, and please get tested if you have any symptoms that could be Covid-19. 

In the meantime, alert level four is the best place for us to be to break those chains of transmission. While we’ll likely see some spread within bubbles, the more of us that stay in our bubbles – and wear masks when we leave out bubbles – the less likely we are to get transmission between bubbles. And remember, vaccinations are continuing, don’t hesitate to book or head along if you’ve got an appointment. 

The crucial thing from here is going to be making sure delta doesn’t start spreading among our essential workers as that would undoubtedly prolong the outbreak.

Keep going!