Epidemiology of influenza over a ten-year period in Belgium: overview of the historical and current evidence

BACKGROUND: Generally influenza, a contagious respiratory disease, leads to mild illness, but can present as a severe illness with significant complications for some. It entails significant health challenges and an economic burden. Annual vaccination is considered the most effective preventive measure against influenza, especially in high-risk groups. METHOD: Epidemiological, demographic and vaccination data of influenza from 2009-to-2019 is collected from Sciensano, the Belgian Institute for Health. Sciensano monitors influenza virus through two surveillances: the Influenza-Like Illness (ILI) surveillance in primary care and the Severe Acute Respiratory Infections (SARI) surveillance in hospital settings. RESULTS: 49.6% [± 8.5] of all ILI-samples tested positive in this period. Influenza A was the dominant circulating type, accounting for 73.7% [± 27.5] of positive samples, while influenza B accounted for 24.3% [± 26.7]. For SARI-surveillance, the average rate of samples tested positive was 36.3% [± 9.3]. Influenza A was responsible for respectively 77.7% [± 23.8] of positive samples and influenza B for 22.2% [± 23.7]. Since 2010, epidemics typically lasted about 9.3 weeks [± 2.7]. From 2012 to 2019 the average vaccine effectiveness was 34.9% [± 15.3]. CONCLUSION: Influenza is quickly considered a trivial disease, but can have substantial repercussions. It remains difficult to identify the level of treat of influenza due to antigenic evolution. Measures to prevent, control and treat are needed. Vaccines that provide broader and more durable protection that can be produced more rapidly could be a potential solution.