Long term follow up of the immunogenicity of 7-valent pneumococcal conjugate vaccine (PCV7) in vulnerable elderly populations at high risk for invasive pneumococcal disease

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Streptococcus pneumoniae is the commonest cause of pneumonia in the community, and a major cause of illness and death in the elderly. A free pneumococcal polysaccharide vaccination (PPV) program was introduced, in Australia, in 2005. However, responses to PPV in the elderly are often poor. A more immunogenic pneumococcal conjugate vaccine (PCV-7) is available for children under 2 but is not licensed for adults. We completed a study that compared the immunogenicity of PCV-7 and PPV in the hospitalised elderly who are at highest risk for pneumococcal disease. Elderly patients admitted to hospital that had not previously received PPV, were recruited and randomised to receive PCV-7 or PPV; those who received PCV-7 received PPV six months later. Results showed no significant differences in response after one dose of each vaccine; severely frail patients have less vigorous response to either vaccine. Final follow up was done at 12 months. To our knowledge there are no data on long term immunogenicity studies beyond 12 months comparing PCV and PPV responses in the elderly. The proposed study is a longer term follow up study of subjects five and ten years after the 12 month follow up period of a completed trial of pneumococcal vaccines in frail elderly people, to determine persistence or waning of immunity in surviving subjects as well as measuring influenza vaccine antibody. It is impractical to measure efficacy in such a group in a clinical trial, due to the low incidence of pneumococcal disease, so proxy measures of efficacy using immunologic surrogates are necessary. The surviving study subjects from the above mentioned study will be contacted and interviewed, a blood sample will be collected from them at their current residence to determine persistence or waning of immunity in surviving subjects as well as measuring influenza vaccine antibody. We seek permission to access hospital medical records to be able to determine rates of readmission and other clinical outcomes of older people and ascertain predictors of readmission. Access to the death register will enable us to determine death date and cause and ensure that no attempts are made to contact deceased participants. Following ethics approval, we will check hospital records to identify any further deaths in the trial cohort. For those patients still thought to be alive, we will then contact their last known GP, and check on vital status and medical presentations not resulting in hospitalisation and vaccinations received. If the GP believes the patient is still alive, we will write to them giving them notice that we wish to contact them to ask them to consider being included in a new long-term follow-up cohort study. In this initial letter we will enclose the patient and Responsible Person information leaflets with the consent form and a pre-paid envelope for them to consent or decline further involvement. There is limited available long-term follow-up data on antibody levels in older persons who have been vaccinated with conjugate pneumococcal vaccines.

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