The 2025 influenza season has started. The influenza season started in week 13 (week starting 24 March 2025) when the influenza detection rate (3-week moving average) from the NICD inpatient pneumonia sentinel surveillance in public hospitals breached the seasonal threshold and remained above the threshold for two consecutive weeks. The season started four weeks earlier as compared to the 2024 influenza season which started in week 17 (week starting 22 April 2024).
Based on data from pneumonia surveillance, this is the earliest start to the influenza season since 2010. As of 10 April 2025 within the pneumonia surveillance programme, the most commonly detected subtype and lineage is influenza A(H3N2) (19/28, 68%), followed by A(H1N1)pdm09 (2/28, 7%), and no cases of B/Victoria. Of the 28 samples that tested positive for influenza, 7 samples (25%) were pending influenza A subtyping results.
Influenza A(H3N2), A(H1N1)pdm09 and influenza B are common seasonal influenza strains in humans. The majority of people with influenza will present with mild illness, usually resolving within 3-7 days. However, influenza may cause severe illness leading to hospitalisation or possibly death, especially among those who are at risk of severe influenza illness or complications. High-risk groups include pregnant women, individuals living with HIV, those with chronic conditions such as diabetes, lung disease, tuberculosis, heart disease, renal disease, and obesity, older individuals (≥aged 65) and children <2 years old. These groups should be encouraged to seek medical help early. Updated guidelines on influenza diagnosis and management are available here.
Influenza vaccination is recommended to protect against infection and severe illness. Ideally the influenza vaccine should be administered prior to the start of the influenza season because it takes about 2 weeks for antibodies to develop following vaccination. However, it is not too late to vaccinate. Individuals at risk for severe illness are strongly encouraged to seek the influenza vaccine from either a public health clinic or privately through general practitioners and pharmacies as soon as possible, as the influenza season is starting. Annual vaccination is needed as the influenza virus is constantly changing and immunity to one vaccine wanes with time. Receiving the vaccine can reduce visits to clinics or doctor’s offices, absenteeism from work and school due to influenza illness, as well as to prevent influenza-related hospitalizations.
To minimise the transmission of seasonal influenza the following non pharmaceutical measures can be applied: avoid close contact with sick individuals, practice proper hygiene including frequent hand washing, avoid touching the mouth, eyes, and nose, and covering coughs and sneezes (preferably into your elbow or a tissue, which should be promptly disposed of away from others). Individuals experiencing flu-like symptoms should stay at home to avoid infecting others. It is advisable to seek medical attention if symptoms do not improve in 3-7 days or if symptoms worsen in that time. Clinicians should include influenza as a possible diagnosis when managing patients with respiratory illness.
