Background data of participants included in the analysis during the epidemic season 2010–11, according to vaccination with Pandemrix in 2009–10 and/or trivalent influenza vaccine (TIV) in 2010–11.

The vaccination status was determined with information given by the study participants during the two study phases 2009–11 and with information from the medical records of the health center of Tampere city or the vaccinators.1Age at start of the follow-up.2Pregnant at enrolment, No (% of women). Information on the pregnancy was not available for 2 women vaccinated with both Pandemrix and TIV and for one unvaccinated woman.3Individuals with at least one of the following underlying medical conditions: a heart or lung disease requiring regular medication, a metabolic disease, chronic liver failure or chronic kidney disease, an immune system disease, a condition whose treatment reduces the immune response, or a chronic neurological or neuromuscular disease.Background data of participants included in the analysis during the epidemic season 2010–11, according to vaccination with Pandemrix in 2009–10 and/or trivalent influenza vaccine (TIV) in 2010–11.