Mumps and the MMR vaccine Evening Standard editorial comment Parents have good reason to be concerned about the possibility of a mumps outbreak in London. The epidemiological history of this infectious disease suggests that mumps is unpleasant but hardly ever fatal to children. In rare cases it causes meningitis or encephalitis; it can also cause infertility in boys. Before there was a vaccine for mumps, it tended to kill no more than five people a year. Yet it is impossible to be certain that half a century of vaccination against the disease will not have weakened our natural immunity...