If you got sick at any point in 2025, you weren’t alone. From seasonal viruses to surprise outbreaks, there were plenty of illnesses spreading in the community. We spoke with viral immunologist, Professor Nathan Bartlett from the University of Newcastle and HMRI’s Infection Research Program to take a closer look at the pathogens and health trends that shaped the year.
COVID-19 maintained a steady, low-level presence throughout 2025.
“While COVID-19 did not drive the major waves seen during the pandemic years, it has become part of the broader mix of respiratory pathogens circulating in the community,” Professor Bartlett explained.
NSW Health data suggests virus levels generally remained low, with moderate peaks in January and June.
Several new variants emerged, including XEC and KW.1.1 early in the year. XFG, NB.1.8.1, PE.1.4 and BA.3.2 increased toward the end of 2025.
Influenza made a noticeable comeback in 2025, particularly in the second half of the year.
“Since the COVID years there has been a lot of disruption to the ‘status quo’ for respiratory pathogens, for example disrupted seasonality,” Professor Bartlett noted. “Influenza and RSV are now co-circulating with SARS-CoV-2, sometimes outside their usual seasonal windows, leading to unpredictable peaks and ‘multi-wave’ respiratory seasons.”
While NSW Health data reflects a traditional winter flu wave, with a July-August peak, there was an unexpected surge in November and December.
The unusual early summer spike has been driven by a new variant of Influenza A (H3N2), called subclade K.
Respiratory syncytial virus (RSV) circulated at relatively low levels overall in 2025, but its impact was not evenly felt across all age groups.
Nearly half of all lab confirmed cases of RSV in NSW were in children aged 0-4 years, according to NSW Health, with bronchiolitis (commonly caused by RSV) hospital admissions in the age group remaining stable compared to 2024.
Several other respiratory pathogens continued to circulate in 2025, contributing to community illness and placing pressure on health services.
Globally, respiratory pathogens like Human Metapneumovirus (hMPV) have re-emerged.
“Since late 2024, hMPV has surged globally, notably in China and North America, causing significant paediatric hospitalisations and raising concerns about severe disease in immunocompromised individuals,” Professor Bartlett said.
He also pointed to Mycoplasma pneumoniae, which caused large outbreaks in 2023 and 2024 in Asia and Europe, before declining in 2025. “These infections often present as ‘walking pneumonia’ and have stressed outpatient care systems.”
And while Rhinovirus often flies under the radar, the common cold remains one of the biggest contributors to illness, accounting for around two-thirds of all respiratory infections seen in the community.
Respiratory viruses weren’t the only culprits making us sick in 2025. One of the largest non-viral outbreaks came from an unexpected source, alfalfa sprouts.
A national recall of Parilla Fresh alfalfa sprouts was issued in November due to Salmonella contamination. The unusual strain of Salmonella affected more than 44 people across Australia, including at least 18 in NSW.
The incident was a reminder that food safety remains an important part of public health.
2025 continued a rising trend of co-infection, where people are infected with more than one pathogen at the same time.
“Mixed infections, both viral-viral and viral-bacterial, have become more common, especially in children under five,” Professor Bartlett said. “Studies report up to 34% of cases involving bacterial-viral co-infections, complicating clinical management.”
Common examples of co-infections include a respiratory virus like RSV or influenza alongside a bacterial infection such as pneumonia or an ear infection.
Concerningly, 2025 brought an increase in illnesses that can be prevented by vaccination around the world, and Australia was not immune to the trend.
“Globally, there has been a dramatic resurgence in vaccine-preventable diseases like Whooping Cough post-pandemic, with some countries reporting 10-fold increases compared to pre-pandemic baselines,” Professor Bartlett said.
There were more than 24,000 cases of Whooping Cough (Pertussis) recorded across Australia this year, with almost 9400 in NSW. While the national total dropped from 57,000 in 2024, the figures were still double what they were in 2019.
There was also a resurgence in measles after years of very low transmission in Australia, with more than 160 cases recorded nationally, including 30 in NSW. That’s an alarming increase from just 57 confirmed cases in 2024.
The last 12 months highlighted that infectious diseases are no longer following predictable patterns. With COVID-19 now part of the broader mix of respiratory pathogens, waves of illness can emerge at unexpected times, making them harder to anticipate.
“This means disease surveillance is more important than ever, allowing for faster reaction time and information dissemination to help protect us all,” Professor Bartlett explained, “but particularly to protect those most at risk of severe disease, including the very young, the elderly, the immunocompromised and people with chronic illnesses.”
FluTracking, a joint initiative of the University of Newcastle, Hunter New England Health and HMRI, is one way people can contribute to public health. By reporting symptoms in just 30 seconds each week, the community can help researchers and health authorities detect outbreaks earlier and respond faster.
2025 showed that staying healthy relies on vaccination, disease surveillance and ongoing research working together to protect the community when new threats emerge.
