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Protecting Communities in
Africa from Pneumococcus
This resource has been developed by the Association for Science Education for their RCUK-funded series
‘Research focused teaching resources to inspire students in STEM Careers’
The global research context
Developing vaccination programmmes to protect
communities against pneumococcal disease
The World Health Organisation estimates
that 800 000 children die from diseases
caused by types of the pneumococcal
bacterium.
There are over 90 different types of the
pneumococcus bacterium so the vaccines
being developed must target a
combination of the most harmful, e.g. the
PCV-7 vaccine protects against seven types
of the bacterium.
Scientists run clinical trials to test the efficacy of the pneumococcal vaccines in different
areas of the world.
Your BIG Research Question…
How could a clinical trial be designed to measure the impact of a
pneumococcal vaccine on community health in Africa?
Research summary
Twenty-one similar-sized villages in the same
region of The Gambia were chosen for this study.
The villages were divided at random into two
groups – experimental group and control group.
In the control villages all of the infants up to 30
months old were given a course of vaccination
with the PCV-7 vaccine; children older than this,
and adults, were given the control vaccine.
In the experimental villages all infants, children
and adults were given the PCV-7 vaccine.
At the start of the investigation a sample of
infants, children and adults in each village had a
swab taken from inside the back of the nose. The
swabs were each used to inoculate a bacterial
culture. If pneumococcus was present, laboratory
technicians identified the pneumococcal
serotypes (to know whether those were
serotypes included in the PCV-7 vaccine or not).
This testing was carried out again in each of the
villages with similar samples of the population
after 6, 12 and 22 months.
The inhabitants of each village, and the
laboratory technicians, did not know which
villages were in the experimental or control
group.
Pneumococcus
The Gambia
Pneumococcus bacteria belong to the species
Streptococcus pneumoniae, and exist as more than 90
different strains or serotypes. Pneumococcus can be found
at the back of the nose and throat of many people, and
especially in children. This is the most important
pneumococcal reservoir and the main route of transmission
between individuals in the community. Healthy individuals
can transmit the pneumococcus to other individuals by
sneezing and coughing. Pneumococcus can give rise to
many different diseases in susceptible people including
community-wide pneumonia.
Vaccines
The PCV-7 vaccine was developed in the United States in
2000 and its use brought about a rapid decrease in the
incidence of pneumococcal disease. The vaccine consists of
seven different sugars found in the cell walls of different
strains of pneumococcus bacteria, which are linked to
protein molecules. When injected, the vaccine triggers an
immune response in T-cells that produce antibodies for the
different sugar antigens. The PCV-7 vaccine is effective
against seven different pneumococcal strains – the seven
most common serotypes in Europe and the United States
before vaccine introduction.
Since this study, PCV-7 has been replaced by newer widerranging vaccines.
Research summary continued
Conditions in Africa are very different to those in the
United States and Europe where vaccines are developed.
Vaccination programmes cannot be copied between
continents without taking account of differences such as:
•
burden of disease (higher in Africa than United States)
•
rate of transmission (spread) (greater in Africa)
•
frequency of different types of the bacterium
(different in Africa)
•
vaccination programme design (in United States a
booster vaccine is given after infancy, which can rarely
happen in Africa).
Scientists carried out a clinical trial to find out how
effective the PCV-7 vaccine is in communities in The
Gambia.
Testing for pneumococcus
Pneumococcus can be found at the back of the
nose and throat of many healthy people, and
especially in children. This is the main route of
spread between people in the community.
Healthy individuals can transmit the
pneumococcus to other individuals by sneezing
and coughing.
In this research, technicians
took swabs from inside the
back of the nose of people in
the trial. The swabs were
each used to inoculate a
bacterial culture.
Questions
1.
2.
3.
4.
How do vaccines protect people from infection by bacteria?
How many cases of pneumococcal disease were there in the
United States in 1999 before the vaccine was introduced in each
age group?
How many cases were there for each age group in 2004, five years
after the introduction of the PCV-7 vaccine?
In which age group was the vaccine most effective?
Types of clinical trial
In a randomised control trial participants are given (at random) either the treatment
being trialled or the control treatment. The control treatment can either be no drug at
all or a harmless substitute (a placebo).
In a single blind trial people are not told whether they are being given the treatment or
are in the control group, so that their behaviour does not change. In a double blind
trial, the scientists do not know either.
In a cluster randomised trial a group of people (a village for example) is given the
treatment or becomes a control group so that the impact on the group can be
monitored. This is important where there is not just an impact on the participant, but
also the people around them.
n
t
S
h
e
e
t
1
b
Questions…
1.
2.
3.
4.
5.
6.
Summarise a practical technique that could be used to collect and grow bacteria samples.
Predict and explain how increasing the number of people with immunity could affect the spread of
pneumococcal disease within that community.
Explain whether a randomised trial or a cluster randomised trial would be better for testing the effectiveness
a pneumococcal vaccine on community-wide protection from the disease.
Should participants in the control group be given no vaccine or a control vaccine? Why?
Based on data from the United States (see Student Sheet 1a), why is it unethical for young children to receive
the control vaccine?
Use your own understanding of gathering data to suggest two ways a trial could be designed to improve
confidence in the data and validity of the conclusions.
Now investigate your Big Research Question...
How could a clinical trial be designed to measure the impact of a pneumococcal vaccine on community health in
Africa?
Going deeper with research data
Age group
Time after
vaccination
(months)
n
t
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h
e
e
Percentage of people testing
positive for
t
vaccinated pneumococcus
strain (%)
2
a
Children
(30 months
to 14 years)
0
6
12
22
Control
44.3
18.8
17.9
19.3
Adults
(15+ years)
0
6
12
22
16.7
4.4
3.9
7.6
Experiment
39.2
13.0
11.6
9.7
15.9
4.2
1.3
0.0
Questions
1. All of the villages in this study initially had high percentages of people carrying pneumococcus bacteria. What
is the overall impact of this vaccination study over time on numbers of people testing positive for
pneumococcus?
2. Describe the effect of vaccination with PCV-7 on a) children (30 months to 14 years); and b) adults (15+ years).
3. Describe the changes in the percentage of people testing positive for pneumococcus in the control villages
over the duration of the vaccination study.
4. Describe the differences between the results for children aged 30 months to 14 years in the experiment
villages and those in the control villages.
5. Suggest an explanation for these differences.
6. Suggest an explanation for the difference in results between adults and children.
n
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S
Going deeper with research data
h
e
The researchers were concerned that by removing some strains of pneumococcus, other strains, enot included in
the vaccine, may increase. This harmful side effect was reported to have happened in the United tStates when
2
PCV-7 was first used.
b
Age group
Time after
vaccination (months)
Children
(30 months
to 14 years)
0
6
12
22
Adults
(15+ years)
0
6
12
22
Percentage of people testing positive for
other pneumococcus strains (%)
Control
Experiment
54.9
57.4
61.2
62.6
42.4
41.2
56.7
63.1
41.7
20.5
25.8
30.3
41.0
27.8
22.2
29.2
Questions
1.
Does the data provide evidence of the vaccination study causing an increase in infection by other strains of
pneumococcus?
2.
In this data, the numbers of people testing positive after 22 months was greater than the number testing
positive after 12 months. Suggest reasons for this finding.
3.
Based on the evidence provided in this study, what would be your recommendations to health authorities
in The Gambia and other sub-Saharan African countries regarding vaccination programmes for
pneumococcus?
Where can science research take you?
Dr Anna Roca works for the MRC Unit The
Gambia.
She is an infectious disease epidemiologist
experienced in leading research groups in Africa.
She leads an independent line of research
focused on how pneumococcal bacteria are
carried and spread before and after the
introduction of pneumococcal vaccination.
For more information on science and STEM careers see www.futuremorph.org.
Useful links
Further information
www.mrc.gm/whole-communities-in-africa-could-be-protected-from-pneumococcus-byimmunising-young-children/
Whole communities in Africa could be protected from pneumococcus by immunising
young children.
Other resources from MRC…
MRC Insight Blog
A wealth of short articles highlighting contemporary medical research.
www2.mrc-lmb.cam.ac.uk/microscopes4schools/resources.php
Microscopes for schools
www.insight.mrc.ac.uk/2015/01/15/stem-cells-in-the-classroom/
Stem cells in the classroom
Acknowledgements
Research paper
Anna Roca , Philip C. Hill, John Townend, Uzo Egere, Martin Antonio, Abdoulie Bojang, Abiodun
Akisanya, Teresa Litchfield, David E. Nsekpong, Claire Oluwalana, Stephen R. C. Howie, Brian
Greenwood, Richard A. Adegbola, ‘Effects of Community-Wide Vaccination with PCV-7 on
Pneumococcal Nasopharyngeal Carriage in The Gambia: A Cluster-Randomized Trial’,
Published: October 18, 2011, DOI: 10.1371/journal.pmed.1001107
http://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1001107
Thank you to Anna Roca and Beate Kampmann for permission to use the photographs
on slides 1, 6, 7, 8 and 9.
Organisations
Medical Research Council – The Gambia Unit
London School of Hygiene and Tropical Medicine
Medical Research Council UK
Research Councils UK