Influenza vaccine effectiveness in preventing out-patient, in-patient and severe cases of laboratory-confirmed influenza.
Clin Infect Dis. 2013 Mar 26;
Authors: Castilla J, Godoy P, Domínguez A, Martínez-Baz I, Astray J, Martín V, Delgado-Rodríguez M, Baricot M, Soldevila N, Mayoral JM, Quintana JM, Galán JC, Castro A, González-Candelas F, Garín O, Saez M, Tamames S, Pumarola T, the CIBERESP Cases and Controls in Influenza Working Group
Abstract
Background.?In most seasons, the influenza vaccine is effective in preventing influenza, but it is not clear whether it is equally effective in preventing mild and severe cases. We designed a case-control study to compare the effectiveness of the influenza vaccine in preventing out-patient, in-patient and severe or fatal cases of laboratory-confirmed influenza. Methods.?Hospitalized patients (n=691) with laboratory-confirmed influenza in the 2010-2011 season recruited in 29 Spanish hospitals were individually matched by age, admission/visit date and province, with an out-patient with laboratory-confirmed influenza and an out-patient control. Severe cases were considered those admitted to intensive care units or who died in the hospital (n=177). We compared the influenza vaccine status of controls and out-patient cases, in-patient cases and severe cases using conditional logistic regression adjusted for potential confounding factors. Severe and non-severe in-patient influenza cases were compared using unconditional logistic regression. Vaccine effectiveness was (1-odds ratio) x100. Results.?Adjusted vaccine effectiveness was 75% (odds ratio [OR]: 0.25; 95% confidence interval [CI], 0.16-0.39) in preventing influenza out-patient cases, 60% (OR:0.40; 95% CI, 0.25-0.63) in preventing influenza-associated hospitalizations, and 89% (OR:0.11; 95% CI, 0.04-0.37) in preventing severe cases. In in-patient cases, influenza vaccination was associated with a lower risk of severe influenza (OR, 0.42; 95% CI, 0.22-0.80). Conclusions.?Influenza vaccination prevented influenza cases and hospitalizations and was associated with a better prognosis in in-patients with influenza. The combined effect of these two mechanisms would explain the high effectiveness of the vaccine in preventing severe cases due to influenza.
PMID: 23532475 [PubMed - as supplied by publisher]