The unexpected timing of flu season in South Australia has sparked curiosity and concern among health experts. While the peak winter season typically brings a surge in flu cases, this year's trend is notably different. South Australia's Chief Public Health Officer, Professor Nicola Spurrier, highlights an "unusual" pattern, noting that flu numbers have only recently started to rise, even as August approaches.
This delay in the usual flu spike is attributed to the unique circumstances of the previous year. Professor Spurrier explains that last year's flu season had two distinct waves: a standard peak in the middle of winter, followed by a second wave around October, as summer approached. The subclade K strain, known as the "Super K" strain, from the northern hemisphere, played a significant role in this second wave. This strain provided some population-level immunity, but, as Professor Spurrier points out, "population immunity wanes over time."
The impact of international travel and the changing seasons on flu patterns is also noteworthy. Adelaide general practitioner Daniel Byrne observes that this year's flu cases are significantly lower than in previous winters, a shift that he attributes to the global travel dynamics. With winter in the northern hemisphere coinciding with summer in the southern hemisphere, the flu's spread is now more closely aligned with our summer months, a stark contrast to the trends of just 15-20 years ago.
While flu cases may be lower, other respiratory illnesses are keeping doctors busy. Rhinovirus, the common cold, and RSV (respiratory syncytial virus) are among the top concerns. RSV, in particular, has led to 5,702 cases in South Australia so far this year, posing a significant risk to young babies, who are often hospitalized due to its highly contagious nature.
The article also touches on the importance of the RSV vaccine, which has been expanded in eligibility. Pregnant women have had free access to the RSV vaccine since February 2025, and newborns who didn't receive protection during pregnancy can receive the monoclonal antibody nirsevimab. More recently, in May, adults over 75 became eligible for the free vaccine, and the WA government expanded this to include those aged 65 and older living in residential aged care. Dr. Byrne advocates for similar expanded eligibility in South Australia, emphasizing the potential cost savings for the health system.
As the year progresses, health authorities will closely monitor RSV case numbers, comparing them across states. This unusual flu trend and the evolving landscape of respiratory illnesses in South Australia underscore the importance of staying informed and taking preventive measures, such as getting vaccinated, to protect public health.
