The 2026 RSV season also started in week 11 (week starting 9 March 2026), when the RSV detection rate in children aged <5 years from inpatient pneumonia surveillance in public hospitals exceeded the seasonal threshold and was sustained for two consecutive weeks (Figure 1B). The influenza and RSV seasons both starting in the same week is an unusual event. Clinicians should be on the alert for a potential high burden of patients with respiratory illness in medical facilities in the coming weeks.

Influenza
The 2026 season marks the earliest start to the influenza season recorded since 2010, based on pneumonia surveillance data. The A(H1N1)pdm09 subtype was the most prevalent among influenza A cases in the pneumonia surveillance programme and public clinics but influenza A(H3N2) is most prevalent in outpatient surveillance in private general practitioner practices (Figure 2). Out of 6 influenza A(H1N1)pdm09 samples sequenced to date 5 were subclade D.3.1 and one was subclade D.3.1.1. Of 11 influenza A(H3N2) samples sequenced to date all were subclade K (J2.4.1). Of 7 influenza B Victoria samples sequenced to date 6 were C.5.6 and one was C.5.1.

Respiratory syncytial virus (RSV)
Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and lower respiratory tract infections (LRTI) in young children and can lead to severe illness in infants. It is highly contagious, primarily spreading through respiratory droplets, and re-infections can occur. Over the past decade (excluding pandemic years 2020 and 2021), the RSV season typically begin in mid-February (week 7), with the onset ranging from late-January to late-February, usually preceding the influenza season. Compared to historical data (excluding the SARS-CoV-2 pandemic period), the start of the 2026 RSV season is approximately 4 weeks later than the average, but similar to 2025 when the season also started late (Figure 1B). Among cases with RSV subgroup available in South Africa in 2026, the RSV-A subgroup has accounted for a majority of cases, followed by a smaller proportion of RSV-B subgroup viruses (Figure 3).

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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.

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Influenza detection rates from week 17 to week 21 in 2024, in the Pneumonia Surveillance Programme, exceeded the average detection rates during the same weeks in previous seasons (2016-2019; 2022). However, it follows a similar trend compared to the 2023 influenza season. Similarly, the proportion of inpatient admissions and outpatient clinic consultations from a private hospital group and a network of general practitioners that are respiratory-related (based on ICD-10 codes, J00-J99) appears to be at a similar level to the peak in 2023. Clinicians should include influenza as a possible diagnosis when managing patients with respiratory illness.

Although the majority of people with influenza will present with mild illness, influenza may cause severe illness, which may require hospitalisation or cause death, especially in individuals who are at risk of getting severe influenza complications. High-risk groups include pregnant women (up to 6 weeks post-partum), 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.

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Influenza viruses are further classified based upon antigenic properties. Humoral immunity to influenza viruses is generally thought to be strainspecific and acquired through infection and/or vaccination. Seasonal influenza epidemics can be caused by evolving virus strains that are antigenically distinct from previously circulating virus strains to which a population has some immunity; this is known as antigenic drift. Uncommonly, a completely new strain of influenza will emerge to which there is little or no existing immunity, this is known as antigenic shift and such novel strains can give rise to influenza pandemics.

Influenza viruses are spread from person-to-person. They can be transmitted by exposure to infectious droplets expelled by coughing or sneezing that are then inhaled by others, or can contaminate hands or other surfaces. The typical incubation period for influenza is 1-4 days. Most persons ill with influenza shed virus (i.e. may be infectious) from a few days before symptoms begin through 5-7 days after illness onset. However, very young children can be infectious for >10 days after illness onset; adults with severe disease (e.g. viral pneumonia) may also shed virus for >10 days, and severely immunocompromised persons can shed virus for even longer. Children have the highest rates of seasonal influenza infection and illness in this group can amplify viral transmission in the community.

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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 at: https://www.nicd.ac.za/wp-content/uploads/2023/05/Influenza-guidelines_-25April-2023-final.pdf

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 never 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. Annual vaccination is needed as the influenza virus is constantly changing and immunity to the 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 prevent influenza-related hospitalizations.

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