Carriage studies - what do they add? Human bacterial challenge experiments as an alternative
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What can carriage studies tell us? Dr Caroline Trotter
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Dr Caroline Trotter's presentation at Meningitis Research Foundation's 2013 conference, Meningitis & Septicaemia in Children & Adults
Transcript of Carriage studies - what do they add? Human bacterial challenge experiments as an alternative
What can carriage studies tell us?
Dr Caroline Trotter
Why do we need carriage studies?• Neisseria meningitidis, Haemophilus influenzae and
Streptococcus pneumoniae are carried in the human pharynx and transmitted through droplets
• Most infections result in a period of carriage and only a small minority result in disease
• Many microbial, host and environmental factors influence the likelihood that a pharyngeal infection will progress to invasive disease and the distribution of clinical cases may not accurately reflect the pattern of transmission
• Knowledge of carriage is essential understanding epidemiology of infection and in rational planning of vaccination strategies.
Transmission of Nm, Hi, Sp
Recovery
Invasion
Acquisition
Colonisation
Exposure
Disease
Epidemiology of carriage• E.g. Meningococcal carriage prevalence by age
Christensen et al, 2010, Lancet ID
Effect of conjugate vaccines• The effect of conjugate vaccines on reducing
vaccine-type carriage in controlled trials or before and after studies is now well established
• Hib, MenC, pneumococcal and most recently MenA
Hib
Gessner & Adegbola, Vaccine 2008
Change in carriage prevalence after vaccination
Neisseria meningitidis
• Reduction in group A carriage following MenAfriVac in Burkina Faso
Kristiansen et al. CID 2013
• Reduction in group C carriage in UK teenagers Maiden et al, JID 2008
Streptococcus pneumoniae
Herd immunity
0
100200
300400
500
600700
800900
1000 Observed cases
Predicted cases (with herd immunity)
Predicted cases (no herd immunity)
Challenges of conventional approaches• Role of and need for carriage studies is widely
appreciated, but…• Many factors can influence the epidemiology of
carriage • Large and expensive studies needed to measure
change in (low) prevalence following vaccination• Before and after studies don’t point to mechanisms
of protection• Immunological correlates of carriage not well
defined
Should we go further?
• Carriage as an endpoint for licensure?• Carriage as a bridge to understand epidemiology
where surveillance poor?• Estimating carriage effect at an earlier time point?
• TpmA…
