In this study, investigators propose to determine the optimal dose and isolate of SPN3 to establish colonisation in the human nasopharynx, as well as improving knowledge of immune responses to SPN3 colonisation. The results from this study will be used to inform development of improved SPN3 vaccines and to inform design of future pneumococcal vaccine RCTs.~To increase the relevance of the EHPC model and its use for assessing future vaccines such as V114, investigators are proposing here to set up an EHPC model with carefully selected non-proprietary SPN3 strains. Investigators will conduct a safety and dose-ranging study to determine the optimum SPN3 strain and dose for colonisation acquisition and confirm the dose in a subsequent larger cohort in a reproducibility study and will study mucosal and systemic immune responses to this serotype and their association with protection against colonisation acquisition and clearance.
The 'Experimental Human Pneumococcal challenge' (EHPC) model is a way of putting drops of bacteria into the nose. Investigators have studied this model of putting bacteria in the nose safely in over 1500 volunteers over the past decade with no serious side effects and now want to test the model using a different strain of the bacteria that is commonly found in the community, SPN3.~The aim of this study is to determine how much pneumococcus is needed to achieve nasal colonisation and how long the bacteria live in the nose for before natural immune responses eradicate them. By doing this, Investigators will then be able to test how well future vaccines prevent colonisation with pneumococcus. Investigators want to learn more about how the immune system responds to nasal colonisation with pneumococcus, again to help with development of new vaccines.