New modelling shows South Australia will experience a peak of about 6,000 COVID-19 cases by the middle of March, when the Adelaide Fringe festival is in full swing.
The modelling by the University of Adelaide also shows that the number of COVID-19 patients in hospital will peak at about 250 a few weeks later.
The state is currently recording about 1,500 cases a week.
Ninety-four virus-related deaths were reported last week, including some that occurred months earlier but were only more recently identified as being related to COVID-19.
Chief Public Health Officer Nicola Spurrier said vulnerable members of the community should be aware of the upcoming spike.
"When the wave starts to go up, that's really the time when you start thinking about perhaps wearing a mask, particularly in our most vulnerable areas such as aged care and disability," she said.
"I'll be in communication with those sectors around that time we start to see those numbers increase."
Australian Medical Association state president Michelle Atchison said she was surprised to hear about the new COVID-19 wave, but said it made sense considering the approaching festivals and waning immunity from vaccination doses issued last year.
"People will be in crowded situations," Dr Atchison said.
"It's more likely that if you're sick you'll be able to spread it to others.
"[There should be] just a note of caution to think about who's around you and not go out if you're sick."
The Adelaide Fringe is the largest arts festival in the southern hemisphere.
More than 700,000 tickets to shows at the festival were sold last year.
The pandemic first hit at the tail end of the 2020 event, and the Fringe festivals in 2021 and 2022 were held with restrictions such as mask wearing, checking in with QR codes, and density limits.
'Still a safe way to do this'
Other popular events during the time of year known as "Mad March", include the Adelaide Festival, Adelaide Writers' Week and WOMADelaide, all of which attract large crowds.
The director of Fringe hub Gluttony, Daniel Michael, said it was "very exciting" not to have government-imposed restrictions this year.
But he said some positives had come out of the pandemic, with more cleaners employed and more outdoor venues used.
Masks will be compulsory and a lower-than-usual capacity will be in place for seven sessions of selected shows on Wednesday nights at Gluttony.
"There are some people who are immunocompromised or there are some people who just feel uncomfortable in crowds still," Mr Michael said.
"So we just wanted to provide an opportunity and be inclusive and say, 'Hey, there is still a safe way for you to do this. You don't need to feel like you can't come to Fringe.'
"Then of course there's the big outdoor stage and then there's two small comedy venues — The Piglet and The Squeaker that are also outdoors."
Epidemiologist Adrian Esterman said the looming wave was a timely reminder to keep up to date with COVID-19 vaccinations.
"What we're seeing is two factors happening here. The first is waning immunity — many people had their last dose many months ago and by now have got little protection against infection," Professor Esterman said.
"The second thing is we've got these new sub-variants that are now in Australia."
Despite this, the 74-year-old — who, by his own admission, is immunocompromised — said the spike in cases would not stop him from enjoying Mad March in the festival city.
"Look, I'm in the highest-risk category but I'm not a hermit," he said.
"I go out and about. Other people can do the same thing as well and do it safely.
"You just need to make sure you're up to date with your vaccination and you need to wear a high-quality face mask in crowded situations. Then your risk is absolutely minimal."
