Children/ young people with diabetes may be at a higher risk of acquiring certain infections. These infections include those caused by a bacterium called the pneumococcus which can cause pneumonia, meningitis and ear infections. In the UK older children with diabetes are given a vaccine against the pneumococcus bug called Pneumovax (or PPS23 for short). Although PPS23 causes a good immune response in children over 2 years of age it is not actually known how well PPS23 protects against infection in children of any age. In addition there is some data in adults and children that PPS23 may result in a reduced response to future doses of pneumococcal vaccines (hyporesponsiveness). Because of the lack of information on how well PPS23 protects and potential hyporesponsiveness the investigators would like to study the use of an alternative vaccine against pneumococcus called Prevenar13 (or pCV13). This vaccine is known to be safe and to work well in babies and young children and there have been no concerns about hyporesponsiveness. It has been approved for use in children up to 17 years of age but there is little information on the size and duration of immune response to PCV13 in children aged 6 years and older.

Inclusion Criteria:

• Diagnosis of T1DM and being followed in the Oxfordshire Children's Diabetes Service.
• Aged between 6 years and 17 years.
• Parent/legal guardian willing and able to give informed consent.
• No previous immunisation with a pneumococcal conjugate vaccine (PCV).
• Willing to allow the General Practitioner to be notified of participation in the study.

Exclusion Criteria:

• Known allergic reaction to the vaccine antigen or any of the excipients.
• Bleeding diathesis or condition associated with prolonged bleeding time that would contraindicate intramuscular injection.