Effect of vaccination on the prevention of influenza-related severe illness in adults attended in a third level hospital during the 2017-2018 epidemic season.

Objectives: The objective of this research was to evaluate the effect of influenza vaccination on the prevention of influenza-related severe cases in adults treated in a third-level hospital during the 2017-2018 epidemic season.

Methodology: A descriptive analysis was performed on the entire population of subjects with a laboratory-confirmed influenza test during the 2017-2018 season. A severe case was defined as a patient treated in one of the Intensive Care Units (ICUs) and/or death. The effect of the vaccine on the adult population was determined by multivariate logistic regression analysis.

Results: Between epidemiological weeks 44/2017 and 19/2018, the hospital's laboratory detected 706 positive samples for influenza virus. Of the 551 confirmed patients aged 18 years or older, forty-three were admitted to one of the ICUs, and 26 died during admission. The explanatory multivariate model has shown that flu vaccination prior to or during the epidemic season was a protective factor for the development of severity [OR:0.27 (0.11-0.65, p=0.004)], adjusted by age [OR: 1.03 (1.01-1.06), p=.04], sex, type of virus (H1N1-pdm09, H3N2 or B virus), Chronic Complex Patient index or Advanced Chronic Disease index.

Conclussions: Influenza vaccination is a protective factor against the development of severity associated with influenza infection in a season when vaccination did not contain the virus with higher epidemic circulation among the population. Flu vaccination should be recommended annually following the guidelines established by the health authorities.