In the future it is likely that we will replace the current schedule of injected vaccines with interventions that interrupt transmission of infections in more subtle ways. The agent that causes meningococcal disease (Neisseria meningitidis) colonises the nasopharynx of individuals. In most people, the bacterium is harmless and survives for months in the nasopharynx, however in a minority of people the bacteria can cause invasive disease.

Simply reducing colonisation amongst target groups may protect them, and the rest of the population as well. In a previous study we investigated cross protective antibodies, and found incidentally that inoculating adult volunteers with Neisseria lactamica, a harmless 'cousin' of N. meningitidis, possibly prevents N. meningitidis carriage. If true this could lead to novel mechanisms of reducing colonisation in targeted groups, possibly in the form of a nasal medication. The proposed study large experimental challenge study funded by Meningitis UK that will aim to establish if N. lactamica does or does not inhibit colonisation by N. meningitidis. We will also determine whether N. lactamica displaces existing N. meningitidis carriage, and whether there are individuals who are innately resistant to any Neisseria carriage. The study will recruit 300 volunteers between the ages of 1830yrs from the two universities in Sheffield. It will involve placing droplets of N.lactamica bacteria into the nose of half our group of volunteers, and a harmless water like solution into the nose of the other half of volunteers. We will carry out nose swabs at intervals over a six month period to establish if the pattern of N.meningitidis carriage is effected by N.lactamica colonisation. If the findings are positive we will perform future mechanistic investigations. A62.

Inclusion Criteria:

• Currently healthy
• Students and university employees from either Sheffield Hallam University or the University of Sheffield between the ages of 18 and 25yrs.
• Fully conversant in the English language
• Able to attend the full protocol timetable

Exclusion Criteria:

• Individuals who are Immunocompromised due to a medical condition
• Individuals taking immune modifying medications (not including inhaled steroids)
• Individuals in close contact with immunocompromised people including medical students with full time clinical attachments.
• Individuals who have an current infection
• Current Smokers
• People with an allergy to yeast extract.