Kwaku Poku Asante

Genetic diversity and protective efficacy of the RTS,S/AS01 malaria vaccine

BACKGROUND The RTS,S/AS01 vaccine targets the circumsporozoite protein of Plasmodium falciparum and has partial protective efficacy against clinical and severe malaria disease in infants and children. We investigated whether the vaccine efficacy was specific to certain parasite genotypes at the circumsporozoite protein locus. METHODS We used polymerase chain reaction-based next-generation sequencing of DNA extracted from samples from 4985 participants to survey circumsporozoite protein polymorphisms. We evaluated the effect that polymorphic positions and haplotypic regions within the circumsporozoite protein had on vaccine efficacy against first episodes of clinical malaria within 1 year after vaccination. RESULTS In the per-protocol group of 4577 RTS,S/AS01-vaccinated participants and 2335 control-vaccinated participants who were 5 to 17 months of age, the 1-year cumulative vaccine efficacy was 50.3% (95% confidence interval [CI], 34.6 to 62.3) against clinical malaria in which parasites matched the vaccine in the entire circumsporozoite protein C-terminal (139 infections), as compared with 33.4% (95% CI, 29.3 to 37.2) against mismatched malaria (1951 infections) (P=0.04 for differential vaccine efficacy). The vaccine efficacy based on the hazard ratio was 62.7% (95% CI, 51.6 to 71.3) against matched infections versus 54.2% (95% CI, 49.9 to 58.1) against mismatched infections (P=0.06). In the group of infants 6 to 12 weeks of age, there was no evidence of differential allele-specific vaccine efficacy. CONCLUSIONS These results suggest that among children 5 to 17 months of age, the RTS,S vaccine has greater activity against malaria parasites with the matched circumsporozoite protein allele than against mismatched malaria. The overall vaccine efficacy in this age category will depend on the proportion of matched alleles in the local parasite population; in this trial, less than 10% of parasites had matched alleles. (Funded by the National Institutes of Health and others.).

Safety and efficacy of the RTS,S/AS01E candidate malaria vaccine given with expanded-programme-on-immunisation vaccines: 19 month follow-up of a randomised, open-label, phase 2 trial

BACKGROUND The RTS,S/AS01(E) candidate malaria vaccine is being developed for immunisation of infants in Africa through the expanded programme on immunisation (EPI). 8 month follow-up data have been reported for safety and immunogenicity of RTS,S/AS01(E) when integrated into the EPI. We report extended follow-up to 19 months, including efficacy results. METHODS We did a randomised, open-label, phase 2 trial of safety and efficacy of the RTS,S/AS01(E) candidate malaria vaccine given with EPI vaccines between April 30, 2007, and Oct 7, 2009, in Ghana, Tanzania, and Gabon. Eligible children were 6-10 weeks of age at first vaccination, without serious acute or chronic illness. All children received the EPI diphtheria, tetanus, pertussis (inactivated whole-cell), and hepatitis-B vaccines, Haemophilus influenzae type b vaccine, and oral polio vaccine at study months 0, 1, and 2, and measles vaccine and yellow fever vaccines at study month 7. Participants were randomly assigned (1:1:1) to receive three doses of RTS,S/AS01(E) at 6, 10, and 14 weeks (0, 1, 2 month schedule) or at 6 weeks, 10 weeks, and 9 months (0, 2, 7 month schedule) or placebo. Randomisation was according to a predefined block list with a computer-generated randomisation code. Detection of serious adverse events and malaria was by passive case detection. Antibodies against Plasmodium falciparum circumsporozoite protein and HBsAg were monitored for 19 months. This study is registered with ClinicalTrials.gov, number NCT00436007. FINDINGS 511 children were enrolled. Serious adverse events occurred in 57 participants in the RTS,S/AS01(E) 0, 1, 2 month group (34%, 95% CI 27-41), 47 in the 0, 1, 7 month group (28%, 21-35), and 49 (29%, 22-36) in the control group; none were judged to be related to study vaccination. At month 19, anticircumsporozoite immune responses were significantly higher in the RTS,S/AS01(E) groups than in the control group. Vaccine efficacy for the 0, 1, 2 month schedule (2 weeks after dose three to month 19, site-adjusted according-to-protocol analysis) was 53% (95% CI 26-70; p=0·0012) against first malaria episodes and 59% (36-74; p=0·0001) against all malaria episodes. For the entire study period, (total vaccinated cohort) vaccine efficacy against all malaria episodes was higher with the 0, 1, 2 month schedule (57%, 95% CI 33-73; p=0·0002) than with the 0, 1, 7 month schedule (32% CI 16-45; p=0·0003). 1 year after dose three, vaccine efficacy against first malaria episodes was similar for both schedules (0, 1, 2 month group, 61·6% [95% CI 35·6-77·1], p<0·001; 0, 1, 7 month group, 63·8% [40·4-78·0], p<0·001, according-to-protocol cohort). INTERPRETATION Vaccine efficacy was consistent with the target put forward by the WHO-sponsored malaria vaccine technology roadmap for a first-generation malaria vaccine. The 0, 1, 2 month vaccine schedule has been selected for phase 3 candidate vaccine assessment. FUNDING Program for Appropriate Technology in Health Malaria Vaccine Initiative; GlaxoSmithKline Biologicals.

Epidemiology of malaria in the forest-savanna transitional zone of Ghana

BackgroundInformation on the epidemiology of malaria is essential for designing and interpreting results of clinical trials of drugs, vaccines and other interventions. As a background to the establishment of a site for anti-malarial drugs and vaccine trials, the epidemiology of malaria in a rural site in central Ghana was investigated.MethodsActive surveillance of clinical malaria was carried out in a cohort of children below five years of age (n = 335) and the prevalence of malaria was estimated in a cohort of subjects of all ages (n = 1484) over a 12-month period. Participants were sampled from clusters drawn around sixteen index houses randomly selected from a total of about 22,000 houses within the study area. The child cohort was visited thrice weekly to screen for any illness and a blood slide was taken if a child had a history of fever or a temperature greater than or equal to 37.5 degree Celsius. The all-age cohort was screened for malaria once every eight weeks over a 12-month period. Estimation of Entomological Inoculation Rate (EIR) and characterization of Anopheline malaria vectors in the study area were also carried out.ResultsThe average parasite prevalence in the all age cohort was 58% (95% CI: 56.9, 59.4). In children below five years of age, the average prevalence was 64% (95% CI: 61.9, 66.0). Geometric mean parasite densities decreased significantly with increasing age. More than 50% of all children less than 10 years of age were anaemic. Children less than 5 years of age had as many as seven malaria attacks per child per year. The attack rates decreased significantly with increasing cut-offs of parasite density. The average Multiplicity of Infection (MOI) was of 6.1. All three pyrimethamine resistance mutant alleles of the Plasmodium falciparum dhfr gene were prevalent in this population and 25% of infections had a fourth mutant of pfdhps-A437G. The main vectors were Anopheles funestus and Anopheles gambiae and the EIR was 269 infective bites per person per year.ConclusionThe transmission of malaria in the forest-savanna region of central Ghana is high and perennial and this is an appropriate site for conducting clinical trials of anti-malarial drugs and vaccines.

Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial

Summary Background The RTS,S/AS01 malaria vaccine targets the circumsporozoite protein, inducing antibodies associated with the prevention of Plasmodium falciparum infection. We assessed the association between anti-circumsporozoite antibody titres and the magnitude and duration of vaccine efficacy using data from a phase 3 trial done between 2009 and 2014. Methods Using data from 8922 African children aged 5–17 months and 6537 African infants aged 6–12 weeks at first vaccination, we analysed the determinants of immunogenicity after RTS,S/AS01 vaccination with or without a booster dose. We assessed the association between the incidence of clinical malaria and anti-circumsporozoite antibody titres using a model of anti-circumsporozoite antibody dynamics and the natural acquisition of protective immunity over time. Findings RTS,S/AS01-induced anti-circumsporozoite antibody titres were greater in children aged 5–17 months than in those aged 6–12 weeks. Pre-vaccination anti-circumsporozoite titres were associated with lower immunogenicity in children aged 6–12 weeks and higher immunogenicity in those aged 5–17 months. The immunogenicity of the booster dose was strongly associated with immunogenicity after primary vaccination. Anti-circumsporozoite titres wane according to a biphasic exponential distribution. In participants aged 5–17 months, the half-life of the short-lived component of the antibody response was 45 days (95% credible interval 42–48) and that of the long-lived component was 591 days (557–632). After primary vaccination 12% (11–13) of the response was estimated to be long-lived, rising to 30% (28–32%) after a booster dose. An anti-circumsporozoite antibody titre of 121 EU/mL (98–153) was estimated to prevent 50% of infections. Waning anti-circumsporozoite antibody titres predict the duration of efficacy against clinical malaria across different age categories and transmission intensities, and efficacy wanes more rapidly at higher transmission intensity. Interpretation Anti-circumsporozoite antibody titres are a surrogate of protection for the magnitude and duration of RTS,S/AS01 efficacy, with or without a booster dose, providing a valuable surrogate of effectiveness for new RTS,S formulations in the age groups considered. Funding UK Medical Research Council.

Efficacy of RTS,S malaria vaccines: individual-participant pooled analysis of phase 2 data

Summary Background The efficacy of RTS,S/AS01 as a vaccine for malaria is being tested in a phase 3 clinical trial. Early results show significant, albeit partial, protection against clinical malaria and severe malaria. To ascertain variations in vaccine efficacy according to covariates such as transmission intensity, choice of adjuvant, age at vaccination, and bednet use, we did an individual-participant pooled analysis of phase 2 clinical data. Methods We analysed data from 11 different sites in Africa, including 4453 participants. We measured heterogeneity in vaccine efficacy by estimating the interactions between covariates and vaccination in pooled multivariable Cox regression and Poisson regression analyses. Endpoints for measurement of vaccine efficacy were infection, clinical malaria, severe malaria, and death. We defined transmission intensity levels according to the estimated local parasite prevalence in children aged 2–10 years (PrP2–10), ranging from 5% to 80%. Choice of adjuvant was either AS01 or AS02. Findings Vaccine efficacy against all episodes of clinical malaria varied by transmission intensity (p=0·001). At low transmission (PrP2–10 10%) vaccine efficacy was 60% (95% CI 54 to 67), at moderate transmission (PrP2–10 20%) it was 41% (21 to 57), and at high transmission (PrP2–10 70%) the efficacy was 4% (−10 to 22). Vaccine efficacy also varied by adjuvant choice (p<0·0001)—eg, at low transmission (PrP2–10 10%), efficacy varied from 60% (95% CI 54 to 67) for AS01 to 47% (14 to 75) for AS02. Variations in efficacy by age at vaccination were of borderline significance (p=0·038), and bednet use and sex were not significant covariates. Vaccine efficacy (pooled across adjuvant choice and transmission intensity) varied significantly (p<0·0001) according to time since vaccination, from 36% efficacy (95% CI 24 to 45) at time of vaccination to 0% (−38 to 38) after 3 years. Interpretation Vaccine efficacy against clinical disease was of limited duration and was not detectable 3 years after vaccination. Furthermore, efficacy fell with increasing transmission intensity. Outcomes after vaccination cannot be gauged accurately on the basis of one pooled efficacy figure. However, predictions of public-health outcomes of vaccination will need to take account of variations in efficacy by transmission intensity and by time since vaccination. Funding Medical Research Council (UK); Bill & Melinda Gates Foundation Vaccine Modelling Initiative; Wellcome Trust.

Randomized controlled trial of RTS,S/AS02D and RTS,S/AS01E malaria candidate vaccines given according to different schedules in Ghanaian children

Background The target delivery channel of RTS,S candidate malaria vaccines in malaria-endemic countries in Africa is the World Health Organisation Expanded Program on Immunization. As an Adjuvant System, age de-escalation and schedule selection step, this study assessed 3 schedules of RTS,S/AS01E and RTS,S/AS02D in infants and young children 5–17 months of age in Ghana. Methodology A Phase II, partially-blind randomized controlled study (blind to vaccine, not to schedule), of 19 months duration was conducted in two (2) centres in Ghana between August 2006 and May 2008. Subjects were allocated randomly (1∶1∶1∶1∶1∶1) to one of six study groups at each study site, each defining which vaccine should be given and by which schedule (0,1-, 0,1,2- or 0,1,7-months). For the 0,1,2-month schedule participants received RTS,S/AS01E or rabies vaccine at one center and RTS,S/AS01E or RTS,S/AS02D at the other. For the other schedules at both study sites, they received RTS,S/AS01E or RTS,S/AS02D. The primary outcome measure was the occurrence of serious adverse events until 10 months post dose 1. Results The number of serious adverse events reported across groups was balanced. One child had a simple febrile convulsion, which evolved favourably without sequelae, considered to be related to RTS,S/AS01E vaccination. Low grade reactions occurred slightly more frequently in recipients of RTS,S/AS than rabies vaccines; grade 3 reactions were infrequent. Less local reactogenicity occurred with RTS,S/AS01E than RTS,S/AS02D. Both candidate vaccines were highly immunogenic for anti-circumsporozoite and anti-Hepatitis B Virus surface antigen antibodies. Recipients of RTS,S/AS01E compared to RTS,S/AS02D had higher peak anti-circumsporozoite antibody responses for all 3 schedules. Three dose schedules were more immunogenic than 2 dose schedules. Area under the curve analyses for anti-circumsporozoite antibodies were comparable between the 0,1,2- and 0,1,7-month RTS,S/AS01E schedules. Conclusions Both candidate malaria vaccines were well tolerated. Anti-circumsporozoite responses were greater with RTS,S/AS01E than RTS,S/AS02D and when 3 rather than 2 doses were given. This study supports the selection of RTS,S/AS01E and a 3 dose schedule for further development in children and infants. Trial Registration ClinicalTrials.gov NCT00360230

Patterns and seasonality of malaria transmission in the forest-savannah transitional zones of Ghana

BackgroundKnowledge of the local pattern of malaria transmission and the effect of season on transmission is essential for the planning and evaluation of malaria interventions. Therefore, entomological surveys were carried out in the forest-savannah transitional belt of Ghana (Kintampo) from November 2003 to November 2005 in preparation for drug and vaccine trials.ResultsA total of 23,406 mosquitoes were caught from 919 traps over the two-year period (November 2003 to November 2005): 54.3% were Culicines, 36.2% Anopheles funestus, and 9.4% Anopheles gambiae. Infection rates with Plasmodiumfalciparum were 4.7% and 1.5% for Anopheles gambiae and Anopheles funestus, respectively. Entomological inoculation rates (EIRs) were 269 infective bites per person per year in the first year (November 2003-October 2004) and 231 the following year (November 2004-November 2005). Polymerase Chain Reaction (PCR) analysis detected only Anophelesgambiae s.s. Nineteen mosquitoes were tested by PCR in the wet season; 16 were S-molecular form, 2 M-molecular form and 1 hybrid (S/M). In the dry season, sixteen mosquitoes were tested; 11 S-molecular form, 2 M-molecular form and 3 S/M hybrids. The frequency of knock down resistance (kdr) genotypes F(R) was 0.60.ConclusionThe dynamics and seasonal abundance of malaria vectors in the Kintampo area was influenced by micro-ecology, rainfall and temperature patterns. Transmission patterns did not differ significantly between the two years (2004 and 2005) and both Anopheles gambiae and Anopheles funestus were identified as effective vectors. EIR estimates in 2004/2005 were between 231 and 269 infective bites per person per year. The information provided by the study will help in planning intensified malaria control activities as well as evaluating the impact of malaria interventions in the middle belt of Ghana.

Evaluation of the Safety and Immunogenicity of the RTS,S/AS01E Malaria Candidate Vaccine When Integrated in the Expanded Program of Immunization

BACKGROUND The RTS,S/AS01(E) malaria candidate vaccine is being developed for immunization of African infants through the Expanded Program of Immunization (EPI). METHODS This phase 2, randomized, open, controlled trial conducted in Ghana, Tanzania, and Gabon evaluated the safety and immunogenicity of RTS,S/AS01(E) when coadministered with EPI vaccines. Five hundred eleven infants were randomized to receive RTS,S/AS01(E) at 0, 1, and 2 months (in 3 doses with diphtheria, tetanus, and whole-cell pertussis conjugate [DTPw]; hepatitis B [HepB]; Haemophilus influenzae type b [Hib]; and oral polio vaccine [OPV]), RTS,S/AS01(E) at 0, 1, and 7 months (2 doses with DTPwHepB/Hib+OPV and 1 dose with measles and yellow fever), or EPI vaccines only. RESULTS The occurrences of serious adverse events were balanced across groups; none were vaccine-related. One child from the control group died. Mild to moderate fever and diaper dermatitis occurred more frequently in the RTS,S/AS01(E) coadministration groups. RTS,S/AS01(E) generated high anti-circumsporozoite protein and anti-hepatitis B surface antigen antibody levels. Regarding EPI vaccine responses upon coadministration when considering both immunization schedules, despite a tendency toward lower geometric mean titers to some EPI antigens, predefined noninferiority criteria were met for all EPI antigens except for polio 3 when EPI vaccines were given with RTS,S/AS01(E) at 0, 1, and 2 months. However, when antibody levels at screening were taken into account, the rates of response to polio 3 antigens were comparable between groups. CONCLUSION RTS,S/AS01(E) integrated in the EPI showed a favorable safety and immunogenicity evaluation. Trial registration. ClinicalTrials.gov identifier: NCT00436007 . GlaxoSmithKline study ID number: 106369 (Malaria-050).

An open label, randomised trial of artesunate+amodiaquine, artesunate+chlorproguanil-dapsone and artemether-lumefantrine for the treatment of uncomplicated malaria.

Background Artesunate+amodiaquine (AS+AQ) and artemether-lumefantrine (AL) are now the most frequently recommended first line treatments for uncomplicated malaria in Africa. Artesunate+chlorproguanil-dapsone (AS+CD) was a potential alternative for treatment of uncomplicated malaria. A comparison of the efficacy and safety of these three drug combinations was necessary to make evidence based drug treatment policies. Methods Five hundred and thirty-four, glucose-6-phosphate dehydrogenase (G6PD) normal children were randomised in blocks of 15 to the AS+AQ, AL or AS+CD groups. Administration of study drugs was supervised by project staff and the children were followed up at r home on days 1,2,3,7,14 and 28 post treatment. Parasitological and clinical failures and adverse events were compared between the study groups. Main Findings In a per-protocol analysis, the parasitological and clinical failure rate at day 28 post treatment (PCF28) was lower in the AS+AQ group compared to the AL or AS+CD groups (corrected for re-infections: 6.6% vs 13.8% and 13.8% respectively, p = 0.08; uncorrected: 14.6% vs 27.6% and 28.1% respectively, p = 0.005). In the intention to treat analysis, the rate of early treatment failure was high in all three groups (AS+AQ 13.3%; AL 15.2%; and AS+CD 9.3%, p = 0.2) primarily due to vomiting. However, the PCF28 corrected for re-infection was lower, though not significantly, in the AS+AQ group compared to the AL or the AS+CD groups (AS+AQ 18.3%; AL 24.2%; AS+CD 20.8%, p = 0.4) The incidence of adverse events was comparable between the groups. Conclusions AS+AQ is an appropriate first line treatment for uncomplicated malaria in Ghana and possibly in the neighbouring countries in West Africa. The effectiveness of AL in routine programme conditions needs to be studied further in West Africa. Trial Registration ClinicalTrials.gov NCT00119145

T Cell Responses to the RTS,S/AS01E and RTS,S/AS02D Malaria Candidate Vaccines Administered According to Different Schedules to Ghanaian Children

Background The Plasmodium falciparum pre-erythrocytic stage candidate vaccine RTS,S is being developed for protection of young children against malaria in sub-Saharan Africa. RTS,S formulated with the liposome based adjuvant AS01E or the oil-in-water based adjuvant AS02D induces P. falciparum circumsporozoite (CSP) antigen-specific antibody and T cell responses which have been associated with protection in the experimental malaria challenge model in adults. Methods This study was designed to evaluate the safety and immunogenicity induced over a 19 month period by three vaccination schedules (0,1-, 0,1,2- and 0,1,7-month) of RTS,S/AS01E and RTS,S/AS02D in children aged 5–17 months in two research centers in Ghana. Control Rabies vaccine using the 0,1,2-month schedule was used in one of two study sites. Results Whole blood antigen stimulation followed by intra-cellular cytokine staining showed RTS,S/AS01E induced CSP specific CD4 T cells producing IL-2, TNF-α, and IFN-γ. Higher T cell responses were induced by a 0,1,7-month immunization schedule as compared with a 0,1- or 0,1,2-month schedule. RTS,S/AS01E induced higher CD4 T cell responses as compared to RTS,S/AS02D when given on a 0,1,7-month schedule. Conclusions These findings support further Phase III evaluation of RTS,S/AS01E. The role of immune effectors and immunization schedules on vaccine protection are currently under evaluation. Trial Registration ClinicalTrials.gov NCT00360230