Parents are being urged to ensure that their children have been given the pneumococcal conjugate vaccine (PCV).
Figures released by the Health Protection Agency (HPA) show that 86% of children have received a PCV jab since it was launched a year ago.
However, the HPA said that the figures mean that one in six children have not been vaccinated.
The body said it believes more than 300 children have avoided contracting serious illnesses such as meningitis, septicaemia, and severe pneumonia as a result of having the injection.
And it said that of these 300 cases, 17 youngsters would have died, and about 30 would have been left with a permanently disability.
Director of immunisation, Professor David Salisbury, said: "That about 300 young children have already been saved the trauma of suffering from a major illness like meningitis shows the importance of vaccinating children against serious illness.
"It is so important for a child to get all their vaccinations, and this success story should serve as a reminder to check that your child's vaccines are up to date."
Health minister Ben Bradshaw added: "These figures are a stark reminder of the importance and benefits of immunisation as we shift the focus of the NHS from a sickness service to a wellbeing service."