Where Does South Africa Stand in the Battle Against Influenza?
Influenza, also known as “flu”, is an acute respiratory infection caused by influenza viruses. Primarily, influenza spreads through respiratory droplets which you breathe in or get from contaminated surfaces.
The most common seasonal influenza strains in South Africa are influenza A(H3N2), A(H1N1)pdm09, and influenza B. Individuals infected with these strains show a wide range of symptoms such as sudden onset of fever, muscle pains and body aches, cough, sore throat, blocked or runny nose and headache.
While the majority of influenza infections cause mild illness, influenza may cause severe disease and death. Groups at an increased risk of severe complications of influenza include pregnant women, persons living with HIV, those with chronic illnesses or conditions such as diabetes, lung disease, tuberculosis, heart disease, renal disease, and obesity, the elderly (65 years and older), and children under the age of two years.
Because of South Africa’s locality and temperate climate, in-country influenza epidemics usually occur between April and October, peaking during the winter months. In an effort to combat the virus, the country established influenza sentinel surveillance programmes and encouraged citizens to get influenza vaccines prior to the peak months.
This influenza surveillance report details influenza activity from weeks 1 through 34 in 2023, using three influenza sentinel surveillance programmes, which are coordinated by the Centre for Respiratory Diseases and Meningitis (CRDM) at the National Institute for Communicable Diseases (NICD).
Materials and Methods
Individuals of all ages meeting the following case definitions are approached for consent and enrolled in the respective surveillance programmes.
Influenza transmission thresholds were calculated using the Moving Epidemic Method (MEM), a sequential analysis using the R language designed to calculate the duration, start, and end of the annual influenza epidemic.
The effectiveness of the trivalent/quadrivalent seasonal influenza vaccine (TIV/QIV) to prevent influenza-associated medically attended acute respiratory illness was assessed using a test-negative, case-control study design.
Influenza virus isolates were antigenically characterised using the haemagglutination inhibition (HAI) assay, with turkey red blood cells used as an indicator system. HAI assays were performed using reference reagents from the CDC IRR 2022-2023 WHO influenza reagent kit.
Results
From 1 January 2023 (week 1) through 26 August 2023 (week 34), 7880 individuals were enrolled with respiratory specimens collected and tested through the three surveillance programmes. Influenza infections were identified in 942 individuals, resulting in an overall infection detection rate of 12% (942/7880). Influenza detections occurred from week 1 through week 34. For influenza single infections where a subtype/lineage could be determined (97%, 915/942), infections were dominated by influenza A(H3N2) (98%, 895/915). Influenza A(H1N1)pdm09 and B/Victoria accounted for only 1% (8/915) and 1% (12/915) of single infections, respectively.
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