Using the self-controlled case series design that allows to control implicitly for potential confounding factors, this study aims at investigating the risk of solid organ transplant rejection (liver, kidney, lung, heart, pancreas) following vaccination with Pandemrix™ in the United Kingdom Clinical Practice Research Datalink GP Online Database (CPRD GOLD). Data from the Hospital Episodes Statistics database will also be used. The effect of seasonal influenza vaccination and of various infections including influenza H1N1 will also be explored.