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Open Access Research article

Effectiveness of the trivalent influenza vaccine in Navarre, Spain, 2010–2011: a population-based test-negative case–control study

Iván Martínez-Baz12*, Víctor Martínez-Artola3, Gabriel Reina4, Marcela Guevara12, Manuel García Cenoz12, Julio Morán5, Fátima Irisarri12, Maite Arriazu12, Esther Albeniz5, Jesús Castilla12 and The Primary Health Care Sentinel Network of Navarre

Author Affiliations

1 Instituto de Salud Pública de Navarra, Leyre 15, 31003, Pamplona, Spain

2 CIBER Epidemiología y Salud Pública, Pamplona, Spain

3 Complejo Hospitalario de Navarra, Pamplona, Spain

4 Clínica Universidad de Navarra, Pamplona, Spain

5 Dirección de Atención Primaria, Servicio Navarro de Salud, Pamplona, Spain

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BMC Public Health 2013, 13:191  doi:10.1186/1471-2458-13-191

Published: 6 March 2013

Abstract

Background

Some studies have evaluated vaccine effectiveness in preventing outpatient influenza while others have analysed its effectiveness in preventing hospitalizations. This study evaluates the effectiveness of the trivalent influenza vaccine in preventing outpatient illness and hospitalizations from laboratory-confirmed influenza in the 2010–2011 season.

Methods

We conducted a nested case–control study in the population covered by the general practitioner sentinel network for influenza surveillance in Navarre, Spain. Patients with influenza-like illness in hospitals and primary health care were swabbed for influenza testing. Influenza vaccination status and other covariates were obtained from health care databases. Using logistic regression, the vaccination status of laboratory-confirmed influenza cases was compared with that of test-negative controls, adjusting for age, sex, comorbidity, outpatient visits in the previous 12 months, health care setting, time between symptom onset and swabbing, period and A(H1N1)pdm09 vaccination. Effectiveness was calculated as (1-odds ratio)x100.

Results

The 303 confirmed influenza cases (88% for A(H1N1)pdm09 influenza) were compared with the 286 influenza test-negative controls. The percentage of persons vaccinated against influenza was 4.3% and 15.7%, respectively (p<0.001). The adjusted estimate of effectiveness was 67% (95% CI: 24%, 86%) for all patients and 64% (95% CI: 8%, 86%) in those with an indication for vaccination (persons age 60 or older or with major chronic conditions). Having received both the 2010–2011 seasonal influenza vaccine and the 2009–2010 pandemic influenza vaccine provided 87% protection (95% CI: 30%, 98%) as compared to those not vaccinated.

Conclusion

The 2010–2011 seasonal influenza vaccine had a moderate protective effect in preventing laboratory-confirmed influenza.

Keywords:
Influenza A virus; H1N1 subtype; Influenza vaccines; Case–control studies; Spain