In 2025, the world faced a myriad of health challenges, from familiar viruses to unexpected outbreaks. HMRI's Professor Nathan Bartlett, a viral immunologist, sheds light on the pathogens and health trends that shaped the year. Here's a breakdown of the key health concerns:
- COVID-19's Ongoing Presence: COVID-19 remained a steady presence throughout 2025, no longer dominating headlines but still part of the respiratory pathogen mix. New variants like XEC, KW.1.1, XFG, NB.1.8.1, PE.1.4, and BA.3.2 emerged, causing concern.
- Influenza's Resurgence: Influenza made a noticeable comeback, particularly in the second half of the year. Disrupted seasonality and co-circulation with SARS-CoV-2 led to unpredictable peaks and multi-wave respiratory seasons. A new variant, Influenza A(H3N2) subclade K, caused an early summer spike.
- RSV's Impact: Respiratory syncytial virus (RSV) circulated at relatively low levels overall, but its impact wasn't evenly distributed. Nearly half of all lab-confirmed RSV cases in NSW were in children aged 0-4 years, with bronchiolitis hospital admissions stable compared to 2024.
- Other Respiratory Pathogens: Several other respiratory pathogens continued to circulate, contributing to community illness. Human Metapneumovirus (hMPV) re-emerged globally, causing significant pediatric hospitalizations. Mycoplasma pneumoniae, which caused large outbreaks in 2023-2024, declined in 2025 but remains a concern.
- Non-Viral Outbreaks: Alfalfa sprouts were responsible for a major non-viral outbreak due to Salmonella contamination, affecting over 44 people across Australia. This highlighted the importance of food safety.
- Co-Infections on the Rise: The trend of co-infections, where people are infected with multiple pathogens simultaneously, continued. Viral-viral and viral-bacterial co-infections, especially in children under five, complicated clinical management.
- Preventable Diseases Resurging: 2025 saw a concerning increase in vaccine-preventable diseases worldwide, including Whooping Cough (Pertussis) and Measles. Australia recorded over 24,000 cases of Whooping Cough and a resurgence in Measles cases, despite low transmission in previous years.
What Can We Learn from 2025?
The year underscored the unpredictable nature of infectious diseases. With COVID-19 integrated into the respiratory pathogen landscape, illness waves can emerge unexpectedly, making them harder to anticipate. Professor Bartlett emphasizes the importance of disease surveillance for faster reaction times and information dissemination to protect vulnerable populations, including the very young, elderly, immunocompromised, and those with chronic illnesses.
