To compare the relative immunogenicity and reactogenicity of the existing 23 valent plain pneumococcal vaccine and a 7 valent pneumococcal conjugate vaccine in healthy UK adults aged 50-80 years, and subsequent antibody persistence and response to boosting.

Inclusion Criteria:

• Written informed consent for participation in the study; ages between 50 and 80 years at recruitment

Exclusion Criteria:

• Lack of adequate comprehension of the information sheet, consent form and study nurse's explanation of the study in order to give informed consent.
• Current participation in any other clinical trial
• Any vaccination in the previous month (except influenza vaccination which can be given at any time during the study)
• Prior pneumococcal conjugate vaccine (PNC)
• 23 valent pneumococcal vaccine(PPV) in last 5 years
• Severe general or local reaction to a previous dose of PNC or PPV
• Patients currently immunocompromised as listed in UK Handbook "Immunisation Against Infectious Disease" ed 1996
• Patients who have received intravenous immunoglobulin in the previous month or who will require replacement intravenous immunoglobulin during the period of the study
• Patients in whom pneumococcal vaccination (PPV) is currently recommended as per the UK Handbook "Immunisation Against Infectious Disease"
• Deferral of vaccination if acute systemic illness or temperature >38C on day of vaccination