Case-control study based on hospitals about seasonal influenza vaccine effectiveness to avoid income associated with laboratory-confirmed influenza virus infection in subjects aged 18 or more during 2011-2020 seasons and the disease burden due to respiratory viruses in patients of any age admitted into the hospitals included in the study (AIV - Fisabio) (HBTNCC)

Influenza and vaccination against influenza have a profound impact on society. Thus, knowing the illness burden due to influenza and the impact of current vaccination programs is necessary to take present and future decisions. On the other hand, given the characteristics of the virus and the vaccine, this information must be generated in a timely and continuous manner, so it is convenient to study several flu seasons in large samples of the population.For this purpose, estimates of the influenza vaccine effectiveness based on information from sentinel medical networks using case-control studies or screening methods are useful.These estimates must be timely, robust and reliable, so that the parts involved can take decisions and assessing the impact of the measures adopted have useful information and quality. This need justifies the performance of phase IV post-authorization effectiveness studies based on the impact of the infection and preventive measures on hospital admissions due to influenza.In our case, it is a case-control study based on a hospital-based system of active surveillance of incident income where the presence of influenza infection is verified with the study's own resources. The methodology of detection of virus infection also allows carrying out a study of the burden of the disease by detecting the incidental income associated with respiratory viruses.