Pandemic Influenza Surveillance in the Valencian Community and Seasonal Influenza Vaccines

Background: Surveillance of Pandemic influenza was carried out in the Valencian Community. Some effectiveness studies of the seasonal vaccine for AnH1N1 virus have presented no consistent results. The objective of the work consists on describing the results of the epidemic surveillance and effectiveness of the seasonal vaccine for pandemic influenza in the weeks 28 to 51, 2009. Methods: We studied the cases in primary care, hospitalized confirmed, Polimerase Chain Reaction (PCR) and viral isolates and vaccine coverage. Vaccine effectiveness was calculated by the Farrington method of screening method, in three age groups, and two periods: vaccinated 2008-9 and 2009-10 seasons. Results: In the first period (weeks 28-40) the incidence rates were highest in the group of 15-64 years (7207 cases), followed by those under 15 years (1596 cases). In the second period (weeks 4547) children under 15 years (28218 cases) were the most affected. In both periods incidence in patients older than 65 years was low (rates of 56,3 and 125,1 respectively). In the studied period (weeks 28 at Si) 5481 cases were confirmed, of those that 1746 (31,8%) were hospitalized. The curve of hospitalization rate showed a profile similar to those in primary care and also in microbiological surveillance of the virus. The vaccine effectiveness in the second period was 25% in adults between 15 and 64 years and 51% in those older than 64 years. Conclusions: There is an age-dependent protection with positive vaccine efficacy in the elderly, although it may be confounded by natural exposure to the virus, previous immunizations or immune response.