Background: Influenza is an acute viral respiratory tract disease in humans, often characterized by fever, headache, myalgia, prostration, coryza, sore throat and cough. Influenza infection is clinically indistinguishable from other respiratory viral diseases without laboratory confirmation. Although outbreaks of the virus have been recognized in high-income countries, data describing the epidemiology and burden of influenza is limited in Ethiopia and other low-and-middle-income countries (LMICs). This study aims to estimate the proportion of confirmed influenza cases among patients presenting with a severe acute respiratory infection (SARI) and influenza-like illness (ILI) to determine its epidemiological distribution and guide surveillance and public health interventions. Method: Surveillance of influenza virus has been ongoing at 20 selected sentinel sites (health facilities) across eight regions and two city administrations throughout Ethiopia for the past decade. This study was based on analysis of data captured from 19 of these health facilities from January 2021 to August 2022. Epidemiological and virological data were collected from patients at these facilities as part of routine surveillance activities. Testing by reverse transcription- quantitative polymerase chain reaction (RT-qPCR) of the laboratory samples was carried-out at the National Influenza Center located at the Ethiopian Public Health Institute (EPHI). Standard World Health Organization (WHO) case definitions were used to detect SARI and ILI patients, and standard case reporting form were used for data capture. Multivariable logistic regression analysis was used to identify factors associated with the positivity of influenza tests, and results are expressed by adjusted odds ratios (AORs). Result: Among the 6,193 SARI and ILI patients included in this study, 11.1% (95 %CI: [10.3 -11.9]) were positive for influenza. Of all positive cases, 62% were identified as influenza A virus (IAV) (61% AH3 and 1% AH1), and 38% were identified as influenza B virus (IBV). Higher influenza positivity was detected among ILI cases (26.4%, 525) compared to the SARI cases (3.8%, 161). Peaks in influenza positivity occurred during the months of February and December. The positivity of influenza test was significantly associated with the age of the patients 2 to 5 years (AOR = 1.61, 95% CI: 1.16 - 2.23), 5 to 15 years (AOR = 3.01, 95% CI: 2.22 – 4.09) and 15 to 50 years (AOR = 2.74, 95% CI: 2.14 – 3.50), those patients detected from Addis Ababa (AOR= 5.1, 95% CI: 3.8 - 5.9), and nasopharyngeal samples (AOR=1.8,95% CI: 1.3, 1.8). Conclusion: The positivity rate for influenza virus during the study period was relatively high in Ethiopia. The influenza positivity rate among SARI and ILI patients varies with season and age group. Particularly AH3 were the predominant strains circulating in Ethiopia during the study period in all regions. Strengthening laboratory capacity and influenza sentinel surveillance to detect influenza and other respiratory pathogens is recommended to allow public health officials to interpret national data, compare trends over time locally and globally, and to be prepared for future outbreaks.

Keywords: Influenza, SARI, Sentinel Site, COVID 19, Ethiopia