Recent publications suggest that a universal vaccine against human influenza might be feasible. The vaccine would be based on the M2 protein of influenza A viruses. As yet application of such a universal vaccine seems to be far away, however, since so far only pre-clinical data in a mouse model have been generated. Furthermore, the M2 protein is only present in influenza A viruses and is known to be a minor viral antigen. In addition it may become more variable when it is exposed to immunity in the vaccinated population.