original article
The
new engl a nd jour nal
o f
medicine
n engl j med 367;24 nejm.org december 13, 2012
2284
A Phase 3 Trial of RTS,S/AS01 Malaria
Vaccine in African Infants
The RTS,S Clinical Trials Partnership
The authors are listed in the Appendix.
All the authors assume responsibility for
the overall content and integrity of the
article. Address reprint requests to Ms.
Sara Mian-McCarthy at PATH Malaria
Vaccine Initiative, Communications and
Advocacy Unit, 455 Massachusetts Ave.
NW, Suite 1000, Washington, DC 20001-
2621, or at smian-mccarthy@path.org.
This article was published on November 9,
2012, at NEJM.org.
N Engl J Med 2012;367:2284-95.
DOI: 10.1056/NEJMoa1208394
Copyright © 2012 Massachusetts Medical Society.
ABSTR ACT
Background
The candidate malaria vaccine RTS,S/AS01 reduced episodes of both clinical and
severe malaria in children 5 to 17 months of age by approximately 50% in an ongoing
phase 3 trial. We studied infants 6 to 12 weeks of age recruited for the same trial.
Methods
We administered RTS,S/AS01 or a comparator vaccine to 6537 infants who were
6 to 12 weeks of age at the time of the first vaccination in conjunction with Ex-
panded Program on Immunization (EPI) vaccines in a three-dose monthly schedule.
Vaccine efficacy against the first or only episode of clinical malaria during the
12 months after vaccination, a coprimary end point, was analyzed with the use of
Cox regression. Vaccine efficacy against all malaria episodes, vaccine efficacy
against severe malaria, safety, and immunogenicity were also assessed.
Results
The incidence of the first or only episode of clinical malaria in the intention-to-treat
population during the 14 months after the first dose of vaccine was 0.31 per person-
year in the RTS,S/AS01 group and 0.40 per person-year in the control group, for a
vaccine efficacy of 30.1% (95% confidence interval [CI], 23.6 to 36.1). Vaccine effi-
cacy in the per-protocol population was 31.3% (97.5% CI, 23.6 to 38.3). Vaccine ef-
ficacy against severe malaria was 26.0% (95% CI, −7.4 to 48.6) in the intention-to-
treat population and 36.6% (95% CI, 4.6 to 57.7) in the per-protocol population.
Serious adverse events occurred with a similar frequency in the two study groups.
One month after administration of the third dose of RTS,S/AS01, 99.7% of children
were positive for anti-circumsporozoite antibodies, with a geometric mean titer of
209 EU per milliliter (95% CI, 197 to 222).
Conclusions
The RTS,S/AS01 vaccine coadministered with EPI vaccines provided modest pro-
tection against both clinical and severe malaria in young infants. (Funded by
Glaxo SmithKline Biologicals and the PATH Malaria Vaccine Initiative; RTS,S
ClinicalTrials.gov number, NCT00866619.)
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RTS,S/AS01 Malaria Vaccine in African Infants
n engl j med 367;24 nejm.org december 13, 2012
2285
C
onsiderable gains have been
achieved in malaria control during the past
decade.
1,2
Nonetheless, malaria remains a
major public health concern. In 2010, an estimat-
ed 216 million cases of malaria and 655,000
malaria-related deaths occurred, with the vast
majority of deaths occurring in African children.
1
The RTS,S/AS01 candidate malaria vaccine tar-
gets the pre-erythrocytic stage of the Plasmodium
falciparum parasite. It was developed to reduce
clinical and severe malaria in African children.
Ideally, it would be administered through the
well-established Expanded Program on Immuni-
zation (EPI).
In 2011, we reported the results for the first
coprimary end point from an ongoing phase 3
trial, which showed that during 12 months of
follow-up, RTS,S/AS01 had an efficacy against
clinical and severe malaria of 55.8% (97.5% con-
fidence interval [CI], 50.6 to 60.4) and 47.3% (95%
CI, 22.4 to 64.2), respectively, among children 5 to
17 months of age at enrollment (per-protocol
analysis).
3
Vaccine efficacy against severe malaria
among children 6 to 12 weeks of age and those
5 to 17 months of age combined was 34.8%
(95% CI, 16.2 to 49.2) during an average of 11
months of follow-up (range, 0 to 22). We now
report on the second coprimary end point from
the same trial: efficacy against clinical malaria
during 12 months of follow-up among infants
6 to 12 weeks of age at enrollment, when RTS,S/
AS01 was coadministered with EPI vaccines.
Methods
STUDY DESIGN
Details of the study methods have been described
previously
3-7
and are provided in the Supplemen-
tary Appendix and the study protocol, both of
which are available with the full text of this ar-
ticle at NEJM.org. This phase 3, randomized,
controlled, double-blind trial is being conducted
at 11 centers in 7 African countries with a range
of malaria-transmission intensity (Fig. S1 in the
Supplementary Appendix). The trial is designed
to evaluate vaccine efficacy, safety, and immuno-
genicity for 32 months after the first dose of
study vaccine in children 6 to 12 weeks of age or
5 to 17 months of age at enrollment. The trial
includes three study groups in each age category:
infants who received three doses of RTS,S/AS01
administered at 1-month intervals and a booster
dose 18 months after the third dose, infants who
received three doses of RTS,S/AS01 at 1-month in-
tervals without a booster dose, and a control group
of infants who received a non-malaria compara-
tor vaccine. The analysis described in this report
combines the first two groups (referred to as the
RTS,S/AS01 group) and compares this group with
the control group
6
14 months after the first dose
of vaccine administered in children 6 to 12 weeks
of age (Fig. S2 in the Supplementary Appendix).
The trial protocol was approved by all relevant
ethics review boards and national regulatory au-
thorities (Tables S1A and S1B in the Supplemen-
tary Appendix). Written informed consent was
obtained from the children’s parents or guard-
ians. The study was undertaken in accordance
with Good Clinical Practice guidelines.
8
STUDY OVERSIGHT
The trial was sponsored by GlaxoSmithKline Bio-
logicals (GSK), the vaccine developer and manu-
facturer, and funded by both GSK and the Pro-
gram for Appropriate Technology in Health (PATH)
Malaria Vaccine Initiative, which received a grant
from the Bill and Melinda Gates Foundation.
All study centers received study grants from the
Malaria Vaccine Initiative, which also provided
funding for authors’ travel and accommodations
related to this trial. All the authors reviewed all
manuscript drafts, approved the final version of
the manuscript, and made the decision to submit
it for publication. No GSK authors were involved in
the collection or analysis of the data; the analysis
was performed by an independent statistician. The
authors had full access to the results. The authors
remain unaware of study-group assignments in
this ongoing trial and do not have access to the
raw data at this point. Details of the contributions
of all the authors to the study are available in the
Supplementary Appendix. The Clinical Trials Part-
nership Committee and Writing Group vouch for
the completeness and accuracy of the data pre-
sented and for the fidelity of this report to the
study protocol.
RANDOMIZATION AND VACCINATION
From December 2009 through January 2011, a to-
tal of 6537 infants 6 to 12 weeks of age were ran-
domly assigned to one of the three study groups
in a 1:1:1 ratio. Three doses of the RTS,S/AS01 or
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2286
the comparator vaccine, meningococcal sero-
group C conjugate vaccine (Menjugate, Novartis),
were coadministered with EPI vaccines according
to the World Health Organization EPI schedule.
9
EPI vaccines comprised a diphtheria–tetanus–
whole-cell pertussis–hepatitis B–Hemo phil us in-
fluenzae type b pentavalent vaccine (Tritanrix HepB
Hib, GSK) and an oral poliovirus vaccine con-
taining serotypes 1, 2, and 3 (Polio Sabin, GSK).
The study and pentavalent vaccines were admin-
istered intramuscularly at different protocol-speci-
fied injection sites.
SURVEILLANCE FOR CLINICAL AND SEVERE MALARIA
Passive surveillance for malaria began at the time
of the first vaccination. Parents or guardians of
the study participants were encouraged to seek
care at a health facility if the child had any signs
of illness, and transportation was facilitated. All
participants who presented to a study facility
with reported or documented fever during the
previous 24 hours were evaluated for malaria.
The primary efficacy end point for this analy-
sis was the incidence of clinical malaria, defined
as an illness in a child who was brought to a study
facility with an axillary temperature of 37.5°C or
higher and P. falciparum asexual para sitemia at a
density of more than 5000 parasites per cubic
millimeter or a case of malaria meeting the pri-
mary case definition of severe malaria (Table S2
in the Supplementary Appendix). Different para-
site thresholds were used for secondary case
definitions (Table 1). Participants who were hos-
pitalized were evaluated for severe malaria on
the basis of a protocol-defined algorithm (Table
S3 in the Supplementary Appendix).
4,10
SAFETY SURVEILLANCE
Data regarding serious adverse events were re-
corded by means of passive surveillance begin-
ning after the first dose of vaccine. Verbal autop-
sies were conducted for deaths that occurred
outside study facilities.
11
Information was col-
lected on all unsolicited reports of adverse events
that occurred within 30 days after vaccination
and on reactogenicity (pain, swelling, redness at
the injection site, drowsiness, fever, irritability or
fussiness, or loss of appetite) within 7 days after
vaccination among the first 200 participants en-
rolled at each center. Symptom intensity was as-
sessed with the use of standardized methods
(Table S4 in the Supplementary Appendix). Infor-
mation on related adverse events within 30 days
after vaccination was collected for all partici-
pants. Study clinicians used clinical judgment to
decide whether an adverse event was likely to be
related to the vaccine. In an analysis of previous
RTS,S studies, rash was observed more frequently
in children vaccinated with RTS,S than in con-
trols.
12
Rashes and mucocutaneous diseases oc-
curring within 30 days after vaccination and sei-
zures occurring within 7 days after vaccination
were reported according to Brighton Collabora-
tion guidelines
13,14
(see the Methods section in
the Supplementary Appendix).
IMMUNOGENICITY
Anti-circumsporozoite antibodies were measured
by means of enzyme-linked immunosorbent
assay
15
in the first 200 infants enrolled at each
study center at screening and 1 month after dose-3.
An antibody titer of 0.5 EU per millimeter or
greater was considered to be positive.
LABORATORY AND RADIOLOGIC PROCEDURES
Laboratory and radiologic procedures have been
reported previously
5
and are described in the
Supplementary Appendix.
STATISTICAL ANALYSIS
The statistical methods have been described in
detail previously.
3,7
We used Cox regression mod-
els (1 minus hazard ratio) to evaluate vaccine ef-
ficacy against the first or only episode of clinical
malaria, using the study center as a stratification
factor that allowed for differential baseline haz-
ards. For the coprimary end point, vaccine effi-
cacy against clinical malaria during 12 months
of follow-up in the two age categories, 97.5%
confidence intervals were used, ensuring an
overall two-sided alpha level of 5%. The propor-
tionality of hazards was evaluated by means of
Schoenfeld residuals and models, including time-
varying covariates. Secondary analyses, which
included evaluations based on other case defini-
tions and an analysis including multiple episodes
of clinical malaria, were performed with the use
of negative binomial regression. Vaccine efficacy
against severe malaria was defined as 1 minus
the risk ratio and is presented with 95% confi-
dence intervals and Fisher’s exact P values.
Primary analyses of vaccine efficacy were
based on the per-protocol population, which in-
cluded all participants who received three doses
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RTS,S/AS01 Malaria Vaccine in African Infants
n engl j med 367;24 nejm.org december 13, 2012
2287
Table 1. Efficacy of the RTS,S/AS01 Vaccine against Clinical and Severe Malaria in Infants Enrolled at 6 to 12 Weeks of Age.
Variable RTS,S/AS01 Vaccine Control Vaccine Protective Efficacy
Protective Efficacy
Adjusted for Covariates*
No. of
Events
Person-
Yr
Event
Rate
No. of
Events
Person-
Yr
Event
Rate % (CI)† P Value % (95% CI) P Value
Clinical malaria‡
Per-protocol population (12 mo after third dose of vaccine)
First or only episode
>5000 parasites/mm
3
and temperature ≥37.5°C
(coprimary end point)
1161 3163 0.37 714 1476 0.48 31.3 (23.6–38.3) <0.001 31.5 (24.7–37.6) <0.001
>0 parasites/mm
3
and measured or reported fever 1475 2921 0.50 879 1328 0.66 32.4 (26.5–37.9) <0.001 32.6 (26.7–38.0) <0.001
>500 parasites/mm
3
and temperature ≥37.5°C 1282 3073 0.42 770 1429 0.54 30.3 (23.7–36.2) <0.001 30.4 (23.8–36.3) <0.001
>20,000 parasites/mm
3
and temperature ≥37.5°C 1005 3256 0.31 630 1535 0.41 31.4 (24.2–37.9) <0.001 31.6 (24.4–38.1) <0.001
All episodes, >5000 parasites/mm
3
and temperature ≥37.5°C 2301 3604 0.64 1626 1790 0.91 32.9 (26.3–38.8) <0.001 33.0 (26.4–38.9) <0.001
Intention-to-treat population (14 mo after first dose of vaccine)
First or only episode, >5000 parasites/mm
3
and temperature
≥37.5°C
1283 4106 0.31 782 1949 0.40 30.1 (23.6–36.1) <0.001
All episodes, >5000 parasites/mm
3
and temperature ≥37.5°C 2615 4688 0.56 1864 2345 0.79 32.9 (26.7–38.5) <0.001
No. of
Infants
No.
Affected
Affected
rate
No. of
Infants
No.
Affected
Affected
rate % (95% CI) P Value
% %
Severe malaria§
Per-protocol population (12 mo after third dose of vaccine)
Primary case definition 3995 58 1.5 2008 46 2.3 36.6 (4.6–57.7) 0.02
Secondary case definition 3995 63 1.6 2008 51 2.5 37.9 (8.3–57.8) 0.01
Intention-to-treat population (14 mo after first dose of vaccine)
Primary case definition 4358 77 1.8 2179 52 2.4 26.0 (−7.4–48.6) 0.09
Secondary case definition 4358 83 1.9 2179 58 2.7 28.4 (−1.9–49.4) 0.06
* In the adjusted analyses, data were stratified according to study site with adjustment for the distance to the nearest outpatient health facility.
† All end points are presented with 95% confidence intervals except for the coprimary end point, which is presented with 97.5% confidence intervals. The coprimary end point was de-
fined as vaccine efficacy against a first or only episode of clinical malaria, according to the primary case definition.
‡ The primary case definition of clinical malaria was an illness in a child brought to a study facility with a temperature of
≥
37.5°C and Plasmodium falciparum asexual parasitemia at a
density of >5000 parasites per cubic millimeter or a case of malaria meeting the primary case definition of severe malaria.
§ The primary case definition of severe malaria was P. falciparum asexual parasitemia at a density of >5000 parasites per cubic millimeter with one or more markers of disease severity
and without diagnosis of a coexisting illness. The secondary case definition of severe malaria was P. falciparum asexual parasitemia at a density of >5000 parasites per cubic millimeter
with one or more markers of disease severity, including cases in which a coexisting illness was present or could not be ruled out. Markers of severe disease were prostration, respirato-
ry distress, a Blantyre coma score of ≤2 (on a scale of 0 to 5, with higher scores indicating a higher level of consciousness), two or more observed or reported seizures, hypoglycemia,
acidosis, elevated lactate level, or hemoglobin level of <5 g per deciliter. Coexisting illnesses were defined as radiographically proven pneumonia, meningitis on analysis of cerebrospi-
nal fluid, bacteremia, or gastroenteritis with severe dehydration.
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2288
of a study vaccine coadministered with EPI vac-
cines and who were included in efficacy surveil-
lance, starting 14 days after the third dose of a
study vaccine. The modified intention-to-treat
population included all participants who received
at least one dose of a study vaccine. In the ad-
justed analyses, vaccine efficacy was adjusted
for study center and distance to the nearest out-
patient facility (≤5 km vs. >5 km). Data were
censored 14 months after the first dose of vac-
cine, or at the date of emigration, withdrawal of
consent, or death.
Serious adverse events were coded from clini-
cian-assigned diagnoses according to the pre-
ferred terms of the Medical Dictionary for Regulatory
Activities
16
and were based on available clinical
and laboratory evidence.
The primary analysis of immunogenicity was
based on the per-protocol population. Anti-cir-
cumsporozoite antibody titers were plotted and
evaluated after the third dose of a study vaccine
on the basis of seropositivity levels and geomet-
ric mean titers.
Results
STUDY POPULATION
In total, 6537 infants 6 to 12 weeks of age were
enrolled; 6003 (91.8%) were included in the per-
protocol analysis (Fig. 1, and Fig. S3 in the Sup-
plementary Appendix). Baseline demographic
characteristics were similar in the two study
groups (Table S5 in the Supplementary Appen-
dix). The numbers of participants and malaria
episodes according to study center are shown in
Table S6 in the Supplementary Appendix. As ex-
pected, the majority of malaria episodes were
reported by centers in areas with the highest
transmission; 43.5% of all clinical malaria epi-
sodes were reported by two high-transmission
sites in western Kenya. These two sites, combined
with the site in Nanoro, Burkina Faso (where
transmission is high but seasonal), accounted for
72.6% of clinical malaria episodes in this analy-
sis. The rate of use of insecticide-treated nets was
85.8% overall and was similar in the two study
groups. Indoor residual spraying was conducted
as a public health intervention at four study cen-
ters; at those centers, spraying coverage was low
(Table S7 in the Supplementary Appendix).
VACCINE EFFICACY AGAINST CLINICAL AND SEVERE
MALARIA
In the per-protocol population, the incidence of a
first or only episode of clinical malaria meeting
the primary case definition during 12 months of
follow-up was 0.37 per person-year in the RTS,S/
AS01 group and 0.48 per person-year in the con-
trol group, for a vaccine efficacy of 31.3% (97.5%
CI, 23.6 to 38.3). Kaplan–Meier curves are shown
in Figures 2A and 2B. Vaccine efficacy was not
constant over time (P<0.001 by Schoenfeld re-
siduals), with efficacy higher at the beginning
than at the end of the follow-up period (Table S8
in the Supplementary Appendix). Vaccine effica-
cy against all clinical malaria episodes was 32.9%
(95% CI, 26.3 to 38.8). Estimates of efficacy
against clinical malaria were consistent across
all case definitions and in both adjusted and
intention-to-treat analyses (Table 1).
At least one episode of severe malaria occurred
in 58 of 3995 infants (1.5%) in the RTS,S/AS01
group and in 46 of 2008 infants (2.3%) in the
control group, for a vaccine efficacy of 36.6%
(95% CI, 4.6 to 57.7) in the per-protocol popula-
tion. In the intention-to-treat population, at least
one episode of severe malaria occurred in 77 of
4358 infants (1.8%) in the RTS,S/AS01 group and
in 52 of 2179 infants (2.4%) in the control
group, for a vaccine efficacy of 26.0% (95% CI,
−7.4 to 48.6) (Table 1, and Tables S15 and S16 in
the Supplementary Appendix).
SAFETY
Serious Adverse Events
Serious adverse events were reported in 17.9% (95%
CI, 16.8 to 19.1) of recipients of the RTS,S/AS01
vaccine and in 19.2% (95% CI, 17.6 to 20.9) of
recipients of the meningococcal vaccine (
Table 2
,
and Table S9 in the Supplementary Appendix). A
total of 94 infants died: 66 of 4358 infants (1.5%;
95% CI, 1.2 to 1.9) in the RTS,S/AS01 group and
28 of 2179 infants (1.3%; 95% CI, 0.9 to 1.9) in the
control group. Causes of death were similar in
the two groups; none of the deaths were thought
to be related to vaccination (Table S10 in the Sup-
plementary Appendix). Serious adverse events that
were considered to be related to a study vaccine
occurred in 7 infants: 4 of the 4358 infants in the
RTS,S/AS01 group and 3 of the 2179 infants in
the control group; 4 events (2 in each group)
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