Is each flu season always the same?

<bold>Introduction:</bold> Influenza viruses typically circulate during fall and winter known as the flu season which begins to increase in October, peaks between December and February. Influenza virus can cause pneumonia and seasonal variations in disease severity can happen. <bold>Aim:</bold> To compare influenza disease severity between prior (October 2022- February 2023) and current (October 2022- February 2023) flu seasons. <bold>Methods:</bold> We included the patients with a positive influenza antigen and/or PCR test at last two flu season. Hospitalized patients with influenza pneumonia were analyzed for mortality, disease severity, ICU need. <bold>Results:</bold> In prior flu season, 1116 patients were tested and 133 (12%) were positive for influenza A and/or B antigen; 170 (27.5%) out of 618 were positive in current season. PCR positivity was detected in 11 patients in prior season and 57 in current season. Mortality was significantly higher in the current flu season (n:24) than the prior season (n:5) (19% vs 8.3%, OR:2.58, p<0.001). Severe influenza pneumonia, supplemental oxygen, and ICU need were more frequent in the current flu season compared to the prior flu season (43.5% vs 23.6%, OR:3.5, p=0.009; 69.6% vs 8.3%, OR:25.2, p<0.001; 31.3% vs 18.3%, OR:2, p=0.036). The most frequent influenza virus subtype was H1N1 (51%) in current season and H3 (63.6%) in prior season. <bold>Conclusion:</bold> Current flu season is more challenging than the previous and that can be explained by the H1N1 subtype.