Dr Caroline Trotter's presentation at Meningitis Research Foundation's 2013 conference, Meningitis & Septicaemia in Children & Adults

1. What can carriage studies
tell us?
Dr Caroline Trotter

2. 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.

3. Transmission of Nm, Hi, Sp
Exposure
Invasion
Acquisition
Disease
Recovery
Colonisation

4. Epidemiology of carriage
• E.g. Meningococcal carriage prevalence by age
Christensen et al, 2010, Lancet ID

5. 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

6. Hib
Change in carriage prevalence after vaccination
Gessner & Adegbola, Vaccine 2008

7. Neisseria meningitidis
• Reduction in group C carriage in UK teenagers
• Reduction in group
A carriage following
MenAfriVac in
Burkina Faso
Kristiansen et al. CID 2013
Maiden et al, JID 2008

8. Streptococcus pneumoniae

9. Herd immunity
Observed cases
Predicted cases (with herd immunity)
Predicted cases (no herd immunity)
19
98
/9
9
19
99
/0
0
20
00
/0
1
20
01
/0
2
20
02
/0
3
20
03
/0
4
20
04
/0
5
20
05
/0
6
20
06
/0
7
20
07
/0
8
20
08
/0
9
1000
900
800
700
600
500
400
300
200
100
0

10. 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

11. 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…