BACKGROUND: This study analyzed the epidemiological trends of three significant respiratory infectious diseases in Taiwan: invasive pneumococcal disease (IPD), influenza with severe complications, and tuberculosis during post-COVID-19 pandemic period. METHODS: We utilized data from Taiwan's Centers for Disease Control and Prevention (CDC) website and classified the COVID-19 prevention policies into three phases for the year 2021, 2022, and 2023. We then performed a statistical analysis of reported case numbers for the three respiratory diseases during the 3-year period using the Kruskal-Wallis test, followed by joinpoint regression model for the identification of seasonal distribution and variation. RESULTS: An annual increase was observed in cases of IPD and influenza with severe complication, with influenza exhibiting a significant surge in 2023 (p <
0.001). IPD showed a non-significant upward trend (p = 0.111), while tuberculosis cases decreased annually (p = 0.114) with the gradual slowdown in the incidence rate reduction. Also, seasonal analysis revealed that IPD peaked in winter and spring, while influenza with severe complication peaked anomalously in the summer of 2023, suggestive of a prominent summer influenza. Finally, imported cases of influenza with severe complication, primarily from East and Southeast Asia, were noted only in 2023. CONCLUSIONS: The relaxation of COVID-19 preventive measures in Taiwan led to a marked resurgence of respiratory infectious diseases, particularly influenza with severe complication, accompanied by anomalous seasonality in 2023. This study highlights the need for continued vigilance and appropriate public health strategies, including vaccination and non-pharmaceutical interventions, to manage respiratory infectious diseases in the post-pandemic era.