Here’s why NSW numbers got so high

The NSW lockdown, first introduced on June 26 and now extended until the end of September, has become more restrictive as COVID-19 case numbers have climbed. So why, after more than two months of lockdown, are case numbers still rising? And what will it take to flatten the curve?

It’s all in the R number

Putting aside some of the factors that shape how fast or slow the virus spreads, the simplest way to understand why case numbers are going up is to look at the “effective reproduction number”, or Reff, as it’s often known.

The Reff refers to the average number of people an infected person passes the virus onto.

This week, NSW Premier Gladys Berejiklian said the Reff in NSW was sitting at 1.3. This means for every 10 people who test positive to COVID-19, you would expect around another 13 people to become infected. As long as the Reff remains above 1, the epidemic will continue to grow.

The number of new daily case numbers will also keep increasing, because the more people that get infected, the more people the virus is passed on to, and on it goes. This is why NSW case numbers have continued to climb, even as the Reff has remained relatively steady.

How Delta changes the game

The idea behind lockdowns is to help mitigate the spread of the virus and get the Reff below 1. So why aren’t public health measures in NSW doing just that?

According to Catherine Bennett, chair of epidemiology at Deakin University, the Delta variant is thought to be at least two times more contagious than previous variants, which makes it harder to control.

The problem is that people are asymptomatic for a couple of days before they know they’re infectious, Professor Bennett said. So by the time they find out they are COVID positive, the people they’ve infected are already infectious. That makes the task of contact tracing enormously difficult.

Did lockdowns come too late?

In addition to the challenges presented by Delta, some experts have argued NSW’s high case numbers are a result of stricter lockdown measures coming too late.

It’s a view held by University of Melbourne epidemiologist Tony Blakely. Professor Blakely said the Delta outbreaks unfolding in Melbourne and Auckland were evidence that even snap, “circuit breaker” lockdowns — which both cities entered within days of COVID-19 being detected — did not necessarily guarantee success.

Part of it, he said, came down to luck.

Professor Bennett agreed, and said even with a “really organised response”, Delta wasn’t always able to be contained, especially if the virus was circulating in the community and the links between cases weren’t clear.

Despite high case numbers and a slower introduction of restrictions, Professor Bennett said the NSW lockdown was still having an effect, and buying important time until vaccination targets were reached.

Vaccine uptake the way out

While lockdowns and contact tracing are helping to suppress the virus in NSW, Professor Bennett said increasing vaccine rates would ultimately reduce transmission and get Delta under control.

“You start to bring case numbers down, and then you get them down to a level — and it’s unlikely to be zero — that your contact tracing and testing is able to cope [with],” she said.

Importantly, vaccination rates in Sydney’s most COVID-ravaged hotspots are growing quickly, but authorities say the benefits of the surge in jabs won’t be seen until mid-September.

Victoria at a crossroads

Professor Blakely said it was very unlikely cases would ever get back to zero in NSW, given the push to reopen.

But in Victoria, he said authorities had a “complex decision” to make about how to manage COVID-19 in the coming weeks and months, before vaccine coverage reached adequate levels to open up.

“Victoria is right on a knife edge,” he said.

“The trends have not been good … we keep seeing mystery cases, and whenever you see mystery cases, there is going to be more COVID out in the community.”

He said if Victoria had not managed to get daily case numbers below five by the proposed end of its lockdown on September 2, authorities had to decide whether to continue to pursue COVID-zero with hard lockdowns, or pivot to “living with the virus” with softer measures.

“Ideally, we re-eliminate [the virus],” he said.

“But it might just be that the societal consensus that living in soft lockdown from now to November, and having some cases but controlling them, is better than living in hard lockdown over half the [period of] time.”