New Zealand’s current cases of covid-19 — the first community outbreak for six months — have been linked to a traveller who arrived from Australia and was taken to Middlemore Hospital earlier this week.

Prime Minister Jacinda Ardern and Director-General of Health Dr Ashley Bloomfield have provided a covid-19 update on day two of the nationwide lockdown, when it was revealed there were now 21 community cases.

Ardern said the current positive cases had been linked via genome sequencing to a traveller who arrived from NSW on a managed red zone flight.

That person returned a positive day one test on August 9 and was moved from the Crown Plaza hotel to the Jet Park facility.

They were then transferred to Middlemore Hospital on August 16.

Ardern said the period in which cases were in the community was relatively short, but new information could change this conclusion.

She said primary lines of investigation were staff at the Crown Plaza, staff at the Jet Park facility and staff involved in their arrival and transport. Middlemore Hospital was not part of the investigation.

Customs were investigating footage and identifying areas of interest and testing staff.

“Nothing has eventuated from this line of inquiry to date,” she said.

Staff at Jet Park and Crown Plaza were being retested.

Watch the update 

Today’s covid media briefing by Prime Minister Jacinda Ardern. Video: RNZ News

Ardern said a family adjacent to the case at the Crown Plaza had now tested positive for covid on their day 12 test.

“That means we’re dealing with a high level of infectivity in this case.”

She said everyone at the Crown Plaza would stay on while the usual protocols were undertaken.

Ardern said while compliance across the managed isolation sites for vaccination had been very high, “we will continue our search in a thorough way across both sites as you would expect”.

Ardern thanked the first positive case for getting tested.

“If it wasn’t for you getting tested when you did, this could be a much much more difficult situation.

“Having said that, we’re prepared for cases to get worse before they get better, that is always the pattern in these outbreaks. But today, we believe we’ve uncovered the piece of the puzzle we were looking for,” she said.

Stamping out ability improved
“That means our ability to circle the virus, lock it down, and stamp it out generally has greatly improved.”

Dr Bloomfield said all cases in the community are being transferred safely to a quarantine facility or are already there.

He said 12 of the 21 cases had already been confirmed as being part of the same Auckland cluster. A further eight wdere currently being investigated.

“These new community cases are not unexpected, as the prime minister said, and we would expect the number of cases to continue to grow in particular because of the large number of locations of interest and the mobility of these cases over the few days before the lockdown started.”

As of this morning, more than 360 individual contacts had been identified, although this did exclude contacts from large settings.

Number will increase
“Through the day-to-day, that number will increase significantly.”

Dr Bloomfield said they were fielding a large number of complaints about people holding gatherings and they were being referred to police.

“As you can see from that update, level 4 is where New Zealand needs to be at the moment,” Ardern said.

Ardern said ministers would meet tomorrow morning to decide the lockdown level for the rest of the country outside Auckland and Coromandel. The decision would be shared at tomorrow’s 1pm update.

This article is republished under a community partnership agreement with RNZ.

Article by AsiaPacificReport.nz

New Zealand has avoided community transmission, even though an Australian visitor tested positive for the delta variant which dominates Australia’s latest covid-19 outbreaks.

New Zealand health authorities were quick to react, isolating and testing contacts and suspending travel. Of the traveller’s 2,609 contacts, 93 percent have now returned a negative test result.

But given the delta variant is up to twice as infectious as the original strain, the unique nature of how covid-19 spreads also partly explains why New Zealand has managed to stave off an outbreak.

Among the factors that influence viral transmission, one variable is often overlooked: the K factor. This describes how a virus spreads in clusters and through superspreading events, and we now know that this is an important aspect of SARS-CoV-2, the virus that causes covid-19.

We have become more familiar with the R numbers — R0 which describes the number of people an infected person will pass the virus on to, on average, if no public health measures are in place, and Re which describes the infection rate once public health measures like masks, social distancing and vaccines have been introduced.

But early studies and modelling of how covid-19 spreads highlight the K factor, suggesting only about 10-20 percent of infected individuals account for 80-90 percent of the total number of cases. This implies that most infected people don’t pass the infection on to others.

Few people do most of the spreading
This pattern of spread triggers superspreading events. It is quite possible the infected tourist belonged to the 80-90 percent of non-spreaders and did not pass the infection on to many other people. He himself may have been infected in a superspreading event in Australia.

New Zealand has successfully eliminated covid-19 and doesn’t have any known clusters, thanks to comprehensive border control and precautionary measures. This means any new cluster or community transmission chain would need several rounds of introduction to get started.

You can think of it in this way. If 10 infectious people arrived in the country, only one would be likely to spread the virus to levels that could outpace contact tracing.

This was shown in a study that used genomic data to trace how the first wave of community transmission took hold in New Zealand. The data not only confirmed the effectiveness of quick public health interventions, but also highlighted the importance of the K factor.

The effective reproductive number, Re, of New Zealand’s largest cluster decreased from 7 to 0.2 within the first week of lockdown. Similarly, only 19 percent of virus introductions into New Zealand resulted in ongoing transmission of more than one additional case.

Vaccination and public health measures
Beyond these considerations, as the infected individual had already received a single vaccine dose in Australia, it is possible this reduced the virulence of the infection.

It is also possible that some of the people he interacted with had also already received one or two doses of the vaccine. We can’t rule out a vaccination effect in keeping the infection mild, or even breaking the chain of transmission.

What can New Zealand do to keep the delta variant at bay? The initial success of New Zealand’s elimination strategy helped to reset the country to a situation where all new variants are imported rather than mutating from existing local infections. This is critical as the rate of mutation is higher during periods of uncontrolled spread. That didn’t happen in New Zealand.

New Zealand’s strict border control and quarantine, even during times of zero community transmission, helped to keep new variants at bay.

Looking ahead, several issues will be critical. New Zealand needs to continue border control measures to keep overseas infections in check. We will need to negotiate travel bubbles based on developments in other countries.

I also support calls for an accelerated vaccination rollout and the continued use of masks in public places and transport. Last but not least, using the contact tracing app is critical here as it helps “reverse contact tracing” to rapidly identify superspreading events.

Dr Arindam Basu is an associate professor of epidemiology and environmental health, University of Canterbury. This article is republished from The Conversation under a Creative Commons licence. Read the original article.

Article by AsiaPacificReport.nz