“Evaluation of the Effectiveness of Seasonal Flu Vaccine for the Past Three Seasons Against H1N1 Flu in Health Workers”

Background: The virus that causes to the Influenza type A (seasonal flu and H1N1 flu), belongs to the family Orthomyxoviridae differentiate into subtypes based on antigenic response of two proteins Haemaglutinina (H) and Neuraminidase (N). The present scientific evidence on the effectiveness of the vaccine of the seasonal flu against H1N1 flu is incomplete and contradictory. Objective: Evaluate the effectiveness of the vaccine of the seasonal flu against H1N1 flu.
Methods: Case-control study, included 68 (n) health workers (HW) of the General Hospital Universitary of Alicante, who consulted by acute illness respiratory symptoms.
Through the immunization register and the Mínimum Data Service of Preventive Medicine, were collected vaccination history of the seasons 2006-2007, 2007-2008 and 2008-2009 of 68 HW.
The diagnosis of H1N1 flu in the HW was realized with the PCR -FT test.
The explanatory variable is the vaccination history and the outcome variable onset of infection with H1N1 flu.
For the association study using the ^x2 test.
The effectiveness is calculated by the odds ratio (OR) with a confidence interval of 95% (CI 95%) and the formula was used EV = 1-OR to evaluate the vaccine efficacy in case-control studies.

Results: The evaluation included 68 HW with acute illness respiratory symptoms, with a mean age of 36.8 years old, 23 HW were diagnosed of H1N1 flu and 45 HW were diagnosed of respiratory infection of different etiology. Of the 23 diagnosed with H1N1 flu, 11 HW (47.8%) had history of vaccination of the seasonal influenza last the 3 years. The 45 HW who did not get sick from H1N1 flu, 15 HW (33.3%) had a history of vaccination against seasonal influenza in the previous 3 years. Were obtained an odds ratio (OR) of 1.833 with CI 95% (0.6-5.1). OR was obtained for each vaccination season obtained an OR of 2.47, 95% CI (0.6-14.4) of the 2006-07 season, an OR of 2.69 with 95% CI (0.9-7.9) of the 2007-08 season and an OR of 2.37 with 95% CI (0.7-7.8) of the 2008-09 season. The calculated OR is above the unit so can not calculate the effectiveness.

Conclusions: The seasonal flu vaccination of health-care workers in the previous three seasons is not effective in preventing novel H1N1flu.