This study aimed to estimate the cost and factors associated with severe hospitalized patients due to influenza in unvaccinated and vaccinated cases. The study had a cross-sectional design and included three influenza seasons in 16 sentinel hospitals in Catalonia, Spain. Data were collected from a surveillance system of influenza and other acute respiratory infections. Generalized linear models (GLM) were used to analyze mean costs stratified by comorbidities and pregnancy. Multivariate logistic models were used to analyze bacterial coinfection, multi-organ failure, acute respiratory distress syndrome, death and ICU admission by season and by vaccination status. Costs of ICU, hospitalization and total mean costs were analyzed using GLM, by season and by vaccination status. All models were adjusted for age and sex. A total of 2742 hospitalized cases were included in the analyses. Cases were mostly aged ≥ 60 years (70.17%), with recommended vaccination (86.14%) and unvaccinated (68.05%). The ICU admission level was statistically significant higher in unvaccinated compared to vaccinated cases. Costs of cases with more than or equal to two comorbidities (Diff = EUR - 1881.32), diabetes (Diff = EUR - 1953.21), chronic kidney disease (Diff = EUR - 2260.88), chronic cardiovascular disease (Diff = EUR - 1964.86), chronic liver disease (Diff = EUR - 3595.60), hospitalization (EUR 9419.42 vs. EUR 9055.45), and total mean costs (EUR 11,540.04 vs. 10,221.34) were statistically significant higher in unvaccinated compared to vaccinated patients. The influenza vaccine reduces the costs of hospitalization. There is a need to focus strategies in recommended vaccination groups.
Keywords: comorbidity; hospital costs; hospitalization; influenza vaccination.