Covid 19 Alpha, Delta, Omicron: The great escapes that could have been outbreaks

Two weeks after a chart-topping British DJ brought Omicron into our community, there’s no sign of secondary cases. Jamie Morton looks at some other memorable close brushes with the virus.

The Defence Force cluster

It will go down as one of the great mysteries of our pandemic: a cluster that somehow stayed tightly-contained, despite involving an unexplained leap between its cases.

November 2020’s Defence Force cluster began with a NZDF staffer at Auckland’s Jet Park quarantine facility, Case A, who most likely passed the virus on to a colleague at a downtown workshop.

“Case B” wasn’t wearing a mask on his flight home to Wellington – and two of his children, who attend separate Lower Hutt schools, were also among close contacts.

Yet he only spread the virus to two others – a person (Case C) he met for lunch at Little Penang restaurant on The Terrace on a Friday afternoon, and another border worker (Case F).

Linked to these four were cases D – an AUT student aged in her 20s working at the A-Z Collections store in downtown Auckland, and E – a person who was lived in the same apartment building as the student.

While scientists established a genomic link to D and E, it was never clear how A and D came into contact – save for the fact the student worked just 82m from a cafe that Case A visited.

Officials found there were dozens of close contacts between all of these cases, not to mention hundreds of casual ones, and a string of problematic locations of interest like schools, cafes and airports.

Case D was at work two days after developing symptoms, although masked, while the NZDF workshop where initial transmission took place was held in an apartment complex used for about 250 personnel working in MIQ.

After more than 22,000 community tests, however, officials were satisfied there weren’t more cases or undetected links in the chain, and the cluster was closed.

The Northland scare

It might seem hard to comprehend now, but this time a year ago, New Zealand had gone more than a month without a single community case.

That changed when, on January 13, 2021, an infected 56-year-old Whangārei woman, who had just returned from months in Europe, was released from MIQ at Auckland’s Pullman Hotel.

By the time her condition had deteriorated, she and her husband had already visited about 30 different places dotted from Mangawhai and Helensville to Dargaville and Whangārei.

They included large, busy stores like The Warehouse, Farmers and Noel Leeming, along with a series of cafes and bars, sparking a scramble to track down contacts.

It was also revealed the returned traveller had been carrying the Alpha variant, the pandemic’s first variant of concern, which was up to 40 to 80 per cent more transmissible.

Despite there having been more than 300 contacts, along with thousands of community tests, the leak didn’t result in any further cases, or an outbreak like the Valentine’s Day cluster a fortnight later.

That near miss may have been because the woman hadn’t attended any genuine super-spreading events like large gatherings, or it could have owed to the fact she had only had just over a dozen close contacts in her week of travel.

Experts also surmised she simply mightn’t have been highly infectious, given her husband tested negative even after spending a period of time close to her.

Covid in the capital

Last June, the country’s first case of community transmission in four months also had the makings of a major outbreak.

Over a weekend trip to Wellington, an infected Australian traveller who had received just one dose of the AstraZeneca vaccine visited a barbershop, bookshop, a pharmacy, a hotel, a supermarket and five cafes and eateries.

Along with that, the man had spent several hours at Jack Hackett’s Irish Pub in Dixon St – fortunately on a quieter Saturday night when there were only 20 to 30 punters indoors – and a surrealist art exhibition at Te Papa earlier that day.

Over the two hours he spent at Te Papa, the museum said up to 2500 others would have come and gone through its doors, including 600 who visited the exhibition.

To add to worries, it happened to be New Zealand’s first close encounter with the Delta variant then spreading across the globe.

The capital swiftly moved to level 2 as Wellingtonians flocked to local testing sites.

Contact tracers were able to identify more than 2500 contacts, including nearly 60 plane passengers – yet just a handful were classified as close contacts.

After a tense week, and with not a single secondary infection, Wellington moved back to level 1.

What makes an outbreak

As we all now well know, it only takes a single stray case to spark a Covid explosion.

The Delta outbreak that brought our elimination utopia to an end stemmed from a single source that somehow jumped from MIQ. The Valentine’s Day and Auckland August clusters similarly originated from chance incursions.

But there have been far more instances where alarming community cases came to nothing.

We might recall the infected MIQ escapee who visited a downtown Auckland supermarket; the two women who travelled across the North Island after receiving a compassionate exemption from quarantine; the case who crossed the Auckland cordon into Northland; or the Covid-positive tourist who visited 11 spots in Queenstown and took a boat cruise in Milford Sound.

More recently, there were fears of an Omicron outbreak when DJ Dimension – real name Robert Etheridge – visited a number of Auckland’s hot spots on Boxing Day, including a nightclub and bar, restaurants, and a jewellery store.

And on New Year’s Eve, a vaccinated reveller with Covid-19 spent three hours at popular Ponsonby Rd nightclub The Longroom, prompting a request for those who were in the bar to isolate and get tested.

As yet, neither event appeared to have spawned fresh infections.

So, what did it take?

“I think it’s a mix of things,” explained Covid-19 modeller Professor Michael Plank, of Te Pūnaha Matatini and Canterbury University.

“Sometimes, it’s just a behavioural thing – whether that person meets up with lots of other people or goes to crowded places, or mostly just stays home. That makes a huge difference in terms of the risk of passing the virus on.

“Another factor is timing, or whether the person’s infectious period happens to coincide with the period when they’re out and about in the community.”

While much about “super-spreading” remains unclear, researchers point to several factors that raise the risk.

They include the amount of virus a person is carrying (viral load) – especially if also coughing, sneezing or talking loud among others – and possibly even individual biological or genetic traits.

The type of variant involved also mattered, Plank said, as did the effect of vaccination.

“With Delta, if you have a population that’s highly vaccinated, it does a lot to reduce risk of passing the virus on,” he said.

“Whereas with Omicron, we know the vaccine is effective at stopping people getting seriously ill, but it’s less effective at stopping them getting infected.”

On top of all that, there was a deal of random variability – and luck – involved.

Epidemiologists have often referred to something called the Pareto principle – otherwise known as the “80-20 rule” – that’s now a well-established phenomenon in virology.

This suggested that 80 per cent of disease transmission events in an epidemic were caused by 20 per cent of people.

That trend was certainly seen in New Zealand’s main outbreak, when one in five adults were responsible for up to 85 per cent of the virus’ spread.

But Otago University virologist Dr Jemma Geoghegan wasn’t so sure that rule still applied now, given that new faster-spreading variants, and the measures we’ve put in place to stop them, have changed the game.

“We’ve also seen that the virus can transmit pretty easily even without direct contact,” she added, noting how transmission had occurred via aerosols during testing in one MIQ corridor, within only a 50-second window.

Plank added that, while we may have again dodged a bullet with the Dimension case, it could have easily played out differently.

“If you keep rolling the dice, eventually you run out of luck – and you get community transmission.”

Source: Read Full Article