South Australia is facing an unconventional respiratory season, with leading health officials warning that a spike in influenza cases is likely on the horizon despite an unusually quiet winter so far.

Chief Public Health Officer Professor Nicola Spurrier revealed that influenza numbers have only recently begun to climb, a delay she describes as highly unusual for mid-to-late August. She attributes the delayed start to a strong level of population immunity built up during a surprise late-summer wave earlier this year.

The 'Super K' Factor

According to Professor Spurrier, a summer spike was driven by the northern hemisphere's subclade K strain, often referred to as the "Super K" strain.

"What that summer wave did was provide our community at a population level with some strong initial immunity to the flu," Professor Spurrier said. "But as we know with infectious diseases, over a period of time, population immunity naturally wanes. That is likely why we are only now starting to see the numbers tick up."

A Changing Viral Landscape

Adelaide general practitioner Dr. Daniel Byrne said active flu cases in clinics have been roughly ten times lower than in typical winter seasons, but warned against complacency.

"The world is changing. With international travel and the rapid spread of viruses around the globe, the traditional gap between northern and southern hemisphere seasons is blurring," Dr. Byrne explained. "Perhaps we are going to start seeing more flu in our summer, which is a total shift from 15 to 20 years ago."

Dr. Byrne urged locals who have put off their annual vaccinations to act quickly. "We might be in for a very late season, so the big advice is that it’s still not too late to get your flu shot."

Calls to Expand Free RSV Vaccines

While influenza has been slow to take off, other respiratory conditions are keeping local clinics incredibly busy. Rhinovirus—the common cold—remains the most prevalent, closely followed by Respiratory Syncytial Virus (RSV).

So far this year, South Australia has recorded 5,702 cases of RSV, a highly contagious respiratory virus that is a leading cause of hospitalisation among young infants.

Currently, the federal National Immunisation Program provides free RSV vaccines to pregnant women to protect newborns, while infants can access immunization through state-funded programs. In May, free access was also extended to adults aged 75 and older.

However, Dr. Byrne is advocating for South Australia to follow Western Australia's lead by expanding free eligibility to include vulnerable adults aged 65 and older living in residential aged care.

"Personally, as a doctor in South Australia, I would love to be able to give those vulnerable people an RSV vaccine, saving our health system a huge amount of money in the process," Dr. Byrne said.

Professor Spurrier said state health authorities will continue to monitor the virus closely. "We will review this year's data and look at the epidemiology across different states to guide our future strategies," she said.