The three superspreading events behind Sydney outbreak

NSW has ruled out a lockdown, but there are fears more superspreader events, coupled with the Delta variant, could bring a world of pain.

Westfield Bondi Junction, a “superspreader” birthday party in Sydney’s southwest, and now, potentially, a Tuesday night dinner at Parliament House.

These are the venues and events that all but three of the 48 cases in Sydney’s ballooning coronavirus outbreak are, in one way or another, now linked to.

Premier Gladys Berejiklian described NSW’s current Covid-19 situation as “the scariest period” her state has experienced since the pandemic again, not only because the virus “is extremely contagious” but because “many people may be forced into isolation in the days ahead” and residents are being called on to display more vigilance “than they have ever been asked to during the course of the pandemic”.

Ms Berejiklian has ruled out a total lockdown for now, because “we know basically where the superspreading events have been, we know where the virus is circulating, and we don’t want to take any further action than what we have now”.

But concerns remain that any more superspreader events could bring a world of pain for the NSW capital.

Speaking to reporters on Wednesday, chief health officer Dr Kerry Chant dismissed comparisons between Sydney’s current situation, at the centre of which is the aforementioned Westfield shopping centre, and the outbreak that occurred over Christmas in the Northern Beaches — but said that the strain and the incidents of “inadvertent contact” through which it has been transmitted is a threat not seen before in the community.

“Every cluster has a unique characteristic and what we saw with the Northern Beaches cluster was a superspreader event … there were two different venues that amplified the transmission and then we were able to get on top of it,” Dr Chant said.

“We were not dealing with Delta at that time. What is particularly concerning is usually we would have seen a retail environment as a low-risk setting.”

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Premier Gladys Berejiklian described NSW’s current Covid-19 situation as “the scariest period” her state has been through since the pandemic began. Picture: NCA NewsWire/Damian Shaw

Bondi Junction’s Westfield has been a venue of significant concern for health officials in Sydney’s current outbreak. Picture: Jenny Evans/Getty Images

While finding this outbreak “as early as they did” has allowed public health officials to catch up to the virus quickly and enabled them to bring it under control, Deakin University chair of epidemiology, Catherine Bennett, said “one or two missed cases could turn things around quickly” because of the mutant strain.

“Current restrictions will help dampen down any spread and minimise chances of any unrecognised cases out there sparking more spreader events,” Professor Bennett told news.com.au.

Asked why there have been more events that have led to mass transmission in this outbreak compared to others, Prof Bennett explained there were multiple factors likely at play, creating “a perfect setting for sharing this virus”.

“The first case [an unvaccinated limo driver for international aircrews, who tested positive to the Delta variant just over a week ago] was probably at his most infectious, and possibly someone very efficient at shedding the virus when he was out and about before he realised he was carrying the virus,” she said.

“Combine that with a variant that is associated with a higher viral load and is more efficient at establishing an infection — so a smaller infecting dose is needed for an exposed person to become infected themselves — and you have a spreader event.”

The birthday party held on Saturday night in Sydney’s southwest, which Dr Chant said is being treated as a “superspreading” event, “may well have included a lot of close contacts indoors”, Prof Bennett said.

The source of infection at the gathering — attended by 30 people, 11 of whom have tested positive so far — is believed to be a man in his 30s, who works in Bondi Junction, hadn’t attended any venues of concern, was asymptomatic when he attended the party and got tested immediately after developing symptoms.

The West Hoxton event was “a perfect setting for sharing this virus, especially [with] a variant that is known to infect 60 per cent more of the close contacts on average than the Alpha variant”.

The changing nature of the virus and people becoming complacent about upholding simple measures like social distancing are also contributing to events of a superspreading nature.

“People standing closer together or stepping into each other’s airspaces has always carried a small risk, even if it doesn’t last for the full 15 minutes in the definition of a close contact,” Prof Bennett said.

“But with Delta, this now has the potential to be a more frequent event, and so distancing becomes more important to reduce our chances of picking up an infecting dose, should someone around us be infectious.”

As the strain becomes more dominant, “any exposure effect is more likely to translate to a new case”, she added, using the fact that 50 per cent of the unvaccinated people at the West Hoxton party have already been infected as an example.

“So it is all the more important to identify contacts and get them into quarantine before they become infectious and increase the exposure sites and next generation of cases.”

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A Tuesday night dinner looks like a potential super spreading event.

Marshall was in attendance and was in close contact with several ministers and staff.

Several people at that dinner have still not been contact by NSW Health https://t.co/svhtEMncQq

— Laura Jayes (@ljayes) June 24, 2021

The fact that such a small number of cases are currently unlinked to previous cases is a “good sign that there are not many earlier cases that have been missed this cluster”, Prof Bennett said, when asked about the prospect of any more superspreader events being connected to this outbreak.

“However, there are at least two, and they may have passed it on to other cases that we don’t yet know about, so there is a risk that other clusters might appear around them,” she said.

“Current restrictions prevent close contact gatherings of this size, and masks in public spaces not only reduce the chance of spread, but also remind us to keep our distance from others.

“The more people getting tested, the better — even if people have not been near known exposure sites themselves, but do have symptoms. This is the best way to make sure no other cases have been missed.”