SD: standard deviation.* Defined as diagnosis with one of following diseases: diabetes, chronic obstructive pulmonary disease, asthma, ischemic heart disease, chronic renal failure, or cancer (excluding non-melanoma skin cancer).Demographic and clinical characteristics of cases and controls.

Characteristics of individuals receiving a booster vaccination.

Defined as diagnosis with one of following diseases: diabetes, chronic obstructive pulmonary disease, asthma, ischemic heart disease, chronic renal failure, or cancer (excluding non-melanoma skin cancer).Model A: Adjusted for age, gender, place of residence;**Model B: Adjusted for Model A variables plus income, comorbidity, A(H1N1)pdm09 priority group, receiving the 2009/10 seasonal influenza vaccine, receiving a pneumococcal vaccine, immunosuppressed, pregnancy, ≥20 physician encounters in the last 5 years, ≥1 hospital admission in the last 5 years; use of antiviral prophylaxis and diagnosis of chronic renal failure.Estimates of the effectiveness (VE) of the adjuvanted A(H1N1)pdm09 vaccine (when received ≥14 days before the index date) against hospitalization due to influenza or pneumonia by certain demographic and clinical characteristics.