Meningococcal bacteria are the most common cause of bacterial meningitis and septicaemia in the UK and Ireland.
Babies and children under the age of 5 are at the highest risk, but there is a secondary peak of disease amongst teenagers.
There are several different groups of meningococcal bacteria that cause disease. The most common disease causing groups are meningococcal A, B, C, W and Y. These are commonly referred to as MenA, MenB, MenC, MenW and MenY.