This report summarises the findings from influenza surveillance in South Africa for the period of weeks 1 through 34 of 2025 and was compiled by the World Health Organization (WHO) National Influenza Centre (NIC) housed at the Centre for Respiratory Diseases and Meningitis (CRDM) of the National Institute for Communicable Diseases (NICD).
During 2025, influenza activity was observed from weeks 2 through 34, with an increased period of activity in the normal winter influenza season although the season began earlier than in previous years. The influenza season started in week 13 (week starting 24 March 2025), peaked in week 20 (week starting 12 May 2025) and ended in week 30 (week starting 21 July 2025).
The influenza season was dominated by subtype A(H3N2), with only few detections of A(H1N1)pdm09 and B/Victoria viruses. The circulating A(H3N2) viruses belonged to clade 3C.2a1b.2a.3a.1 (2a.3a.1), together with the 2025 southern hemisphere vaccine strain (A/Croatia/10136RV/2023); and were predominantly subclade J.2.2. Antigenic characterisation using ferret antisera showed that the majority of 2025 A(H3N2) viruses were well inhibited by clade 2a.3a.1 (vaccine type) antisera, with <10% showing low reaction.
Highlights
South Africa is a southern hemisphere country with a temperate climate and with influenza epidemics usually occurring between April and October, with a peak during the winter months.
Epidemiology
- This report includes data from individuals meeting syndromic case definitions within three sentinel respiratory illness surveillance programmes: Viral Watch influenza-like illness (VW) surveillance in outpatients at private general practitioners (n=1194), Influenza-like Illness (ILI) Surveillance Programme in outpatients at public health clinics (n=1123) and the Pneumonia Surveillance Programme in hospitalised patients (n=2839). Together, the three surveillance programmes contributed data from all nine provinces in South Africa.
- Influenza activity was observed from weeks 2 through 34, with an overall detection rate from 30 December 2024 through 24 August 2025 of 10.4% (538/5156). Using the Moving Epidemic Method (MEM) the levels of activity did not surpass the low level in both the ILI and Pneumonia Surveillance programmes. Influenza infections where a subtype/lineage could be determined were dominated by A(H3N2) (96.8%, 508/525). A(H1N1)pdm09 (2.7%, 14/525) and B/Victoria (0.6%, 3/525) only accounted for a small proportion of cases.
- Vaccine coverage in the VW programme was low (3.4%, 26/768). After adjusting for age and timing within the season, the vaccine effectiveness (VE) for any influenza in individuals of all ages was 51.3% (95% confidence interval (CI) -31.3%; 86.0%). For A(H3N2), the adjusted VE was 49.3% (95% CI -36.9%; 85.5%).
For more up-to-date information on influenza, visit the influenza disease index page here.
