Comparison between the characteristics and outcomes of patients hospitalized for COVID-19 in three waves of the pandemic: a retrospective analysis.

BACKGROUND: COVID-19 occurred in successive waves driven by different SARS-CoV-2 variants and shaped by vaccine availability and public health measures. This study analyzes differences in clinical characteristics and outcomes of hospitalized patients across three waves in Brazil. METHODS: This retrospective cohort study included adult COVID-19 patients admitted to 41 hospitals across six Brazilian states from March 2020 to August 2022. Data on demographics, clinical characteristics, and outcomes were collected from medical records and compared across three pandemic waves. Categorical variables were analyzed using Chi-square or Fisher's exact tests, with post hoc Z tests and Bonferroni correction. Continuous variables were analyzed using Analysis of Variance (ANOVA) with Tukey's test or Kruskal-Wallis with Dunn's test and Bonferroni correction. RESULTS: Among 18,632 patients, 37% were hospitalized during the first wave, 55% in the second, and 8% in the third. The median age decreased during the second wave but increased in the third (60 vs 58 vs 66 years; P < 0.001). A higher proportion of patients with three or more comorbidities were admitted during the third wave (15.9% vs 11.9% vs 20.6%; P < 0.001). Anosmia, ageusia, and fever were less frequently reported in the third wave (P < 0.001). Intensive care unit admissions (38.7% vs 37.1% vs 25.5%; P < 0.001) and in-hospital mortality (21.3% vs 23.7% vs 18.2%; P < 0.001) declined throughout the pandemic. CONCLUSION: Clinical manifestations and outcomes evolved across the pandemic waves. The third wave demonstrated fewer chemosensory symptoms, lower severity at admission, and reduced mortality, despite an older and more comorbid patient population.