Impressive success has been achieved worldwide with population based immunisation programmes against several serious infectious diseases. This success is being threatened: the incidence of previously frequent, potentially devastating diseases decreases as a consequence of successful immunisation programmes and attention of the public shifts towards true and alleged "side effects" of vaccines. This can lead to the dilemma of waning public confidence in the necessity, tolerability and safety of vaccinations. Therefore, continuous evaluation of risks and benefits of vaccines is required and results of these need to be communicated broadly to strengthen the confidence in immunisation programmes.