How long can we ride this Covid horse called Luck?
A cluster of factors, including a dose of luck and a famous maths rule bandied around boardrooms, are standing between us and an outbreak. Eugene Bingham reports.
On a sleepy Sunday afternoon, the country was shaken from it’s Covid-19 stupor with news the dreaded South African variant was out in the wild.
People who’d been infected in managed isolation, despite all the precautions they’d taken, were unwitting carriers as they drove around, shopped, ate out. This was the stuff of the community outbreak nightmare which had haunted us since flour and toilet roll supplies were restocked last time.
At each update from DirectorGeneral of Health Dr Ashley Bloomfield we studied his face for signs of hope. And as the week wore on, we detected a glimmer: had we somehow avoided the worst scenario?
In fact, we’ve done a lot of that. Recently published research has revealed less than 20 per cent of New Zealand’s cases led to ongoing transmission; most fizzled out.
Why? The answers lie in a tangle of reasons: from a quick public health and science response; compliant behaviour; the weather; even a maths principle you’re more likely to hear bandied around the boardroom. And plain old good luck. ‘‘Certainly part of it is luck,’’ says Dr David Welch, of Auckland University. ‘‘So any effort that we can make to take the luck out of it, we should be doing.’’
In other words: luck is a horse you can only ride for so long. Eventually, you fall off.
Welch is a senior lecturer in the Department of Computer Science, with a PhD in applied mathematics. He loves numbers and understanding how diseases spread. Last month, Welch was coauthor of a study, led by Otago University’s Dr Jemma Geoghegan, which examined the genomic sequences of hundreds of cases.
Studying the genetic entrails of a virus which has dominated our lives for the past year revealed the patterns and dynamics; how what began with an incursion in Auckland last February was repeated around Aotearoa.
The team looked at 649 virus genomes, from the first known case (February 26) to May 22.
‘‘When we were looking at the genomes, you could build a family tree and see which ones clustered together,’’ says Welch. Scientists could tell which infections were the result of local transmission, and which ones had come across the border – and stopped.
The study showed New Zealand’s outbreak was linked to 277 separate cases. Of those, about 24 per cent were ‘‘singletons’’, where the disease was passed to just one other person. Nineteen per cent were responsible for multiple transmissions; the outbreaks and clusters we became familiar with.
But the vast majority – 57 per cent – went nowhere. The carrier did not infect another person.
‘‘Part of it was because of the controls we had in place,’’ says
Welch. ‘‘By mid-March people had the idea that if you were coming from high-risk areas you should self-isolate.’’
Welch also says, in some ways, it’s what was expected thanks to something you might have heard if you work in sales, or hang out around those who design engineering and control systems: the Pareto principle.
Named after an Italian economist Vilfredo Pareto, it’s also sometimes called the 80/20 rule, a pattern of distribution that fits many scenarios.
In 1896, Pareto found about 80 per cent of land was owned by 20 per cent of the population. It’s a pattern others have observed elsewhere: in business, 80 per cent of sales come from 20 per cent of customers; in sports, 80 per cent of wins will be by 20 per cent of players or teams; and in quality control, and health and safety.
So Welch was hardly surprised to find a small number of people were connected to a large number of cases.
‘‘It’s a well-known principle and it’s been observed in a bunch of different epidemiological situations.’’
So, did our cases this week, the people infected at the Pullman Hotel, just fall on the right side of the maths? Was it just luck?
Welch says luck is part of it. ‘‘But to say dumb luck is unfair to these people who are coming out of quarantine and doing the right things.
‘‘Certainly in the Northland case it was noted she kept a very good record of where she was going. I expect she was being careful about touching others and social distancing where possible.’’
Community testing, contact tracing efforts, and genomic testing all help enormously, too. But what else is going on? Welch says there are a lot of factors we still don’t understand. Seasonality, for instance, seems to play a role.
‘‘You don’t need a fancy model to look at how the number of cases in the Northern Hemisphere really dropped off over summer. It wasn’t that they were doing a great job over summer and dropped the ball over autumn – it’s the way these viruses work.’’
There are a range of possible explanations, says Welch.
‘‘Is it the fact people are indoors [in winter], does the air have different moving qualities, is it that there’s higher UV in summer?’’
So it could be that summer is helping save us from an outbreak. Does that mean we need to be extra careful over coming months?
Welch is blunt: ‘‘Everybody should be worried, and we should be making sure our border facilities and protocols are as tight as possible to avoid a large outbreak.’’
Geoghegan, a virologist and senior lecturer at Otago, agrees we need to be on guard, particularly because of the new variants.
The new varieties – from the UK, South Africa, and Brazil – have mutations that make the spike protein of the virus more likely to attach itself to a host. They’re ‘‘stickier’’ and give an infected person more of a ‘‘viral load’’.
‘‘A viral load is basically the amount of virus being replicated and produced in the host,’’ says Geoghegan. ‘‘If you have a higher viral load, you are probably shedding more of the virus and are more contagious.’’
Shedding is when the body releases tiny infectious fragments through coughing, sneezing, or even breathing and talking. It’s why masks are recommended, and why Canadian Prime Minister Justin Trudeau infamously talked about the dangers of ‘‘speaking moistly’’.
A small study by scientists in Korea, published this week, looked at how long people continued to shed the virus after the onset of symptoms. The average was seven days, but for some patients it was 12 days.
With the new variants giving people a higher viral load, there’s a terrible vicious circle. Some studies show the new variants are between 30-70 per cent more transmissible.
But, again, why do tests so far show the Northland case didn’t even pass the virus on to her husband?
Geoghegan is cautious – more testing is needed. But, she says, it fits with the 80/20 rule. Beyond that, there are a lot of unknowns.
‘‘We don’t know if that is to do with the host or the virus or the environment.
‘‘Most of the clusters we had were associated with a superspreading event or environment which would help the virus, for example the Bluff wedding or conferences and hospitality venues and care homes.
‘‘So environment is obviously very important.’’
For Welch, it comes back to the maths.
‘‘The outcomes we’re getting are dominated by chance,’’ he says. More needs to be done to reduce the risk of infection being passed on, particularly in the isolation facilities.
Maybe it’s time to build purpose-built facilities, rather than relying on hotels, he says. It might cost a lot, but less than the impact of another lockdown.
And, besides, he points out, if we built proper facilities now, we would have them for the future.
‘‘Because we do expect pandemics to become more frequent – this is the third coronavirus we’ve had in 10 years.’’
More grim numbers.
‘‘Everybody should be worried, and we should be making sure our border facilities and protocols are as tight as possible to avoid a large outbreak.’’ Dr David Welch