BMC Public Health
26 October 2011
Dear Editors,
We are grateful to the peer reviewers for their thorough and favourable review of our
manuscript entitled “Primary vaccination with the 10-valent pneumococcal non-typeable
Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in infants in Mali and
Nigeria: a randomized controlled trial”.
Please find enclosed the manuscript amended according to the peer reviewers’ and editorial
comments together with responses to each of the comments.
We hope that these sufficiently address the reviewers’ and editorial queries and concerns
and look forward to receiving your final decision.
Sincerely yours,
Prof. Alassane Dicko
Malaria Research and Training Center
Faculty of Medicine, Pharmacy and Dentistry
University of Bamako
P.O. Box 1805, Bamako, Mali
Email: adicko@icermali.org
Telephone: +223 6674 2296
Fax: +223 2022 7440
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MS: 1943687502575314
Dicko et al. Primary vaccination with the 10-valent pneumococcal non-typeable
Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) in infants in Mali and
Nigeria: a randomized controlled trial
Reviewer’s comments
Reviewer 1: This is a well designed and written clinical trial data conducted at two sites in
two different West African countries - Nigeria and Mali. The data indicate for the first time
that Synflorix is immunogenic in an African population and does not interfere with the
immune responses to routine EPI vaccines. However there a few minor essential revisions
required.
1. The authors intended to enrol 345 but got 365. This needs explanation as it has ethical
implications.
Response: It was initially planned to enrol 230 subjects in Mali and 115 in Nigeria.
Enrolment started earlier in Mali because of logistical challenges in Nigeria. To ensure the
total target sample size for both countries combined (345 infants) would be reached, it was
decided to continue enrolment in Mali until recruitment had started in Nigeria. As a result, 8
additional subjects were enrolled in Mali. In Nigeria, 12 more subjects than planned were
enrolled, of whom 7 were not randomized and did not receive the study vaccine for reasons
given in Figure 1. This resulted in a total of 13 additional subjects enrolled and randomized
(8 in Mali and 5 in Nigeria). There was some reluctance to withhold vaccination with PHiDCV from these children for whom informed consent had already been provided, since PHiDCV had in the mean time been licensed in Europe. Consequently, these subjects remained
in the study.
The following explanation for the 13 additional subjects enrolled and randomized has been
added to the first paragraph under ‘Study Participants’ in the Results section:
‘Subject recruitment started first in Mali and to ensure that the total target sample size would
be reached, enrolment in that country continued until recruitment was also initiated in
Nigeria. As a consequence, 8 more subjects than planned were enrolled and randomized in
Mali. In Nigeria, 5 more subjects than planned were enrolled and randomized. There was
some reluctance to withhold vaccination with PHiD-CV from these infants for whom informed
consent had already been provided, since PHiD-CV had in the mean time been licensed in
Europe.’
2. The trial was conducted at two different sites and the numbers enrolled at each site were
not indicated. This is essential for planning of similar work in future.
Response: The numbers enrolled and randomized in Mali and Nigeria are now included in
the first sentence of the Results section.
3. The Figure one has some texts missing in the boxes. It will also be nice to include in
Figure 1 the reasons for withdrawal for the ten enrolled subjects.
Response: As the text in the boxes of Figure 1 is complete, we consider that there might
have been a formatting problem with the version reviewed. The reasons for withdrawal of the
10 subjects are now provided in a footnote to Figure 1. Please note, as now also indicated in
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Figure 1, that these are the same 10 subjects that were excluded from the ATP
immunogenicity cohort because of absence of serological data post-dose 3.
4. There is a need for the authors to compare data from the two sites, particularly as
reactogenicity and safety outcome measures were determined by different categories of
health care providers (physicians and field workers) in the two countries.
Response: The study was not designed and powered to compare results from the two sites
but rather to assess immunogenicity, reactogenicity and safety following primary vaccination
with PHiD-CV in children in sub-Saharan Africa. Therefore, we do not think that comparative
analysis between the two sites is appropriate in this primary analysis and reporting of the
study data.
5. In the discussion authors explained the high proportion with protective titers of antibodies
pre-vaccination to be due to early exposure to the pneumococcus. Could maternal antibody
transfer be also contributory to this?
Response: We agree that maternal antibody transfer appears to be the most likely
explanation for the high pre-vaccination levels for antibodies against several vaccine
serotypes. We have therefore amended the text in the Discussion (end of second paragraph)
as follows:
‘The high proportions of infants with a pre-vaccination antibody concentration ≥0.2 µg/mL we
observed in this study for several vaccine serotypes can probably be explained by maternal
antibodies transferred during the last months of pregnancy rather than early exposure to S.
pneumoniae, given that antibody concentrations and percentages of infants with antibody
concentration ≥0.2 µg/mL significantly declined in the control group by the time of postvaccination blood draw at approximately 5 months of age. Our data however indicate that
the presence of these high levels of maternal antibodies did not hamper immune responses
to early infant PHiD-CV primary vaccination. It is well known that pneumococcal exposure
and acquisition of pneumococcal nasopharyngeal carriage may start very early in subSaharan infant populations (Levine & Greenwood 2008; O’Brien & Dagan 2003) and recent
publications have indicated that pneumococcal colonization at the time of primary
vaccination could possibly have a negative impact on infant pneumococcal conjugate
vaccine responses (Dagan et al 2010; Vakevainen et al 2010; Madhi et al 2011). Our results
therefore seem to support the need to maintain early vaccination with pneumococcal
conjugate vaccines in this population.’
Reviewer 2:
This is an overall well written manuscript describing the immunogenicity of PHiD-CV
following a primary three dose series of 6, 10 and 14 weeks of age.
Specific comments:
1. The authors should indicate that although randomized, this was an open-labelled trial.
Response: The open-labeled design of the study is indicated in the first sentence of the
Methods section, with the wording ‘this phase III, randomized, open, controlled study’, and in
the Abstract Methods section.
2. The subjects that were withdrawn (2nd sentence of the results section) are not clearly
indicated in the Figure 1. This should be edited accordingly.
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Response: The reasons for withdrawal are now provided in a footnote to Figure 1.
3. Table 1 should include the age at which the 2nd, 3rd vaccines were provided, as well as
the age at which the immunogenicity blood draw was undertaken. In addition, it would be
useful to provide the weight-for-age Z-score at least for the timepoint of the immunogenicity
blood draw to help gain an understanding of the nutritional status of the population.
Response: The mean ages at each vaccine dose are now provided in Table 1, as well as
the mean weight at each dose and the mean interval between dose 3 and the blood
sampling visit. As weight was not recorded at the timepoint for the immunogenicity blood
draw, we calculated weight-for-age Z-scores (based on the WHO Child Growth Standards)
at the time of the three vaccination visits (dose 1-3). These data have been added to Table
1. A brief description has also been added to the text (Results, end of the section on study
participants). Most of the subjects had Z-scores between -2 and 2, 15/217 subjects in the
PHiD-CV group and 11/112 in the control group had a Z-score ≤-2. This low number did not
allow us to make a meaningful evaluation of the effect of nutritional status on immune
responses.
4. Pg 13 -end of the 1st paragraph. The rational for the high antibody in the control group to
select serotypes more likely reflects increase antibody acquisition from the mother (as the
GMCs and proportion with antibody concentration >=0.2 declines by the time of subsequent
immunogenicity blood draw). As such the rational for early vaccination in this population
needs to be re-considered.
Response: As stated in our response to Reviewer 1’s comment #5, we have amended the
text in the Discussion accordingly.
Formatting changes:
1.) Ethics - Please document within the methods section of your manuscript the specific
name of the organization that granted ethical approval to your study going ahead.
*Ethics: Experimental research that is reported in the manuscript must have been performed
with the approval of an appropriate ethics committee. Research carried out on humans must
be in compliance with the Helsinki Declaration (http://www.wma.net/e/policy/b3.htm), and
any experimental research on animals must follow internationally recognized guidelines. A
statement to this effect must appear in the Methods section of the manuscript, including the
name of the body which gave approval, with a reference number where appropriate.
Response: The names of the relevant ethics committees are now provided in the text
(Methods section, last two sentences under ‘Study Setting, Participants and Ethics’).
2.) Trial registration number: Please also include the Trial registration number at the end of
the Abstract in the submission system.
Response: The trial registration number (ClinicalTrials.gov identifier: NCT00678301) is
provided at the end of the Abstract.
3.) Abstract: Please can you ensure that your Abstract contains the context information and
aims of the study in the Background section.
Response: The Background section of the Abstract has been expanded to provide context
information, as well as the aims of the study, as follows:
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‘Pneumonia is still the leading cause of death among children in Africa and pneumococcal
serotypes 1 and 5 are frequently isolated from African children with invasive pneumococcal
disease below the age of 5 years. The immunogenicity, safety and reactogenicity of 3-dose
primary vaccination with the 10-valent pneumococcal non-typeable Haemophilus influenzae
protein D conjugate vaccine (PHiD-CV) were evaluated in infants in Mali and Nigeria.’
4.) Figure cropping: It is important for the final layout of the manuscript that the figures are
cropped as closely as possible to minimise white space around the image. For more
information, see the instructions for authors: http://www.biomedcentral.com/info/ifora/figures.
Response:
The figures have been cropped as closely as possible.
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