Invasive meningococcal disease, when the bacteria enter the bloodstream via the mucous membrane, can cause serious, even life-threatening meningitis or septicaemia with a mortality rate of around 7%. A further 20% of invasive meningococcal infections result in permanent damage such as hearing loss or amputations. Meningococcal infections can occur at any age. However, infants and young children are most frequently infected, followed by adolescents and young adults. Transmission occurs through close contact, mainly as a droplet infection.