New South Wales records 1 million Covid-19 cases in just over two months

New South Wales took 731 days to officially reach 1 million Covid-19 cases. To get from there to 2 million, it took just 75.

The unofficial number might have reached that milestone even sooner.

NSW Health yesterday recorded 15,683 new Covid cases, taking the state's tally to over 2m since the start of the pandemic.

It's an official number, but the actual number of cases is probably far higher.

NSW Health Minister Brad Hazzard said on Wednesday - shortly before he contracted the virus - that cases were estimated to be under-reported by about 50 percent owing to people not being symptomatic or not reporting mild cases.

Based on that logic, the 2m milestone would have been reached about three weeks ago.

John Kaldor, head of global health at the Kirby Institute at the University of NSW, said 50 percent under-reporting was probably at the bottom of the plausible estimates.

It equates to up to a third of the NSW population having had Covid, assuming the rate of reinfection - otherwise known as people who have had the virus twice - is very low.

A spokesperson for NSW Health said the state's reinfection rate was not known.

The pace at which NSW went from 1m infections to 2m was driven by the Omicron variant and the easing of social distancing restrictions.

NSW Health data showed that while the Delta variant represented 43 percent of cases between November and February, the Omicron variant then took over and it now represented 100 percent of cases.

Health and government authorities in NSW have consistently urged people to focus on Covid-19 hospital data, as opposed to case numbers, as the state transitions to living with the virus.

But Professor Kaldor said knowing the number of cases was important because it helped authorities plan.

"We will need to know whether there's going to be a surge in demand on hospital services and intensive care," he said.

He said case numbers were also important for devising the next stage of the vaccine strategy, including which demographics would be asked to get a fourth jab next.

There have been more than 2500 Covid-19 deaths in NSW since the start of the pandemic.

NSW Health data shows about 1 percent of people who caught the early variants, or the Delta variant, died.

The death rate has been much lower, around 0.1 percent of cases, since late November when the Omicron variant emerged.

Similarly, hospitalisation rates with Omicron have been lower, around 1 percent of cases, compared with 10 percent of cases during the Delta outbreak.

Professor Kaldor said Australians now regarded the pandemic as "part of normal life", but that did not mean it was over.

"What Covid has shown us over the last more than two years is its ability to shift," he said.

"The virus changes and its characteristics change and then the response needs to change.

"While we can hope that it will continue to get milder, it may evolve to a form that is either more severe, in terms of the illness that it causes, or more able to elude the vaccine protection."

He said there was no evidence to suggest a variant causing more severe disease, whether in vaccinated or unvaccinated people, had evolved, but the potential was always there.

While Australia kept case numbers low through the first two years of the pandemic, other countries recorded the 1-million-cases milestone much faster.

The US took just three months to reach 1m cases.