Host immune response to A(H1N1)pdm09 vaccination and infection: A one-year prospective study on six cohorts of subjects

► Single dose of A(H1N1)pdm09 vaccine stimulates antibody mean lives of 8.35 months. ► Natural infections had lower antibody level and longer duration than vaccination. ► Pre-vaccination with seasonal flu vaccine led to antibody reduction to A(H1N1)pdm09 virus. ► Pre-vaccination with A(H1N1)pdm09 had no effect on seasonal influenza vaccination.