Samuel Adjei

Bernhard Nocht Institute for Tropical Medicine, Hamburg, Hamburg, Germany

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Publications (21)227.41 Total impact

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    ABSTRACT: 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 Expanded 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 efficacy in the per-protocol population was 31.3% (97.5% CI, 23.6 to 38.3). Vaccine efficacy 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 protection against both clinical and severe malaria in young infants. (Funded by GlaxoSmithKline Biologicals and the PATH Malaria Vaccine Initiative; RTS,S ClinicalTrials.gov number, NCT00866619.)
    New England Journal of Medicine 12/2012; 367(367):2284-2295. · 54.42 Impact Factor
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    ABSTRACT: An ongoing phase 3 study of the efficacy, safety, and immunogenicity of candidate malaria vaccine RTS,S/AS01 is being conducted in seven African countries. From March 2009 through January 2011, we enrolled 15,460 children in two age categories--6 to 12 weeks of age and 5 to 17 months of age--for vaccination with either RTS,S/AS01 or a non-malaria comparator vaccine. The primary end point of the analysis was vaccine efficacy against clinical malaria during the 12 months after vaccination in the first 6000 children 5 to 17 months of age at enrollment who received all three doses of vaccine according to protocol. After 250 children had an episode of severe malaria, we evaluated vaccine efficacy against severe malaria in both age categories. In the 14 months after the first dose of vaccine, the incidence of first episodes of clinical malaria in the first 6000 children in the older age category was 0.32 episodes per person-year in the RTS,S/AS01 group and 0.55 episodes per person-year in the control group, for an efficacy of 50.4% (95% confidence interval [CI], 45.8 to 54.6) in the intention-to-treat population and 55.8% (97.5% CI, 50.6 to 60.4) in the per-protocol population. Vaccine efficacy against severe malaria was 45.1% (95% CI, 23.8 to 60.5) in the intention-to-treat population and 47.3% (95% CI, 22.4 to 64.2) in the per-protocol population. Vaccine efficacy against severe malaria in the combined age categories was 34.8% (95% CI, 16.2 to 49.2) in the per-protocol population during an average follow-up of 11 months. Serious adverse events occurred with a similar frequency in the two study groups. Among children in the older age category, the rate of generalized convulsive seizures after RTS,S/AS01 vaccination was 1.04 per 1000 doses (95% CI, 0.62 to 1.64). The RTS,S/AS01 vaccine provided protection against both clinical and severe malaria in African children. (Funded by GlaxoSmithKline Biologicals and the PATH Malaria Vaccine Initiative; RTS,S ClinicalTrials.gov number, NCT00866619 .).
    New England Journal of Medicine 11/2011; 365(20):1863-75. · 54.42 Impact Factor
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    ABSTRACT: Using segregation analyses, control of malaria parasites has previously been linked to a major gene within the chromosomal region 5q31-33, but also to complex genetic factors in which effects are under substantial age-dependent influence. However, the responsible gene variants have not yet been identified for this chromosomal region. In order to perform association analyses of 5q31-33 locus candidate single nucleotide polymorphisms (SNPs), 1015 children were recruited at the age of 3 months and followed monthly until the age of 2 years in an area holoendemic for Plasmodium falciparum malaria in Ghana. Quantitative (incidence rates of malaria episodes) and qualitative phenotypes (i.e. 'more than one malaria episode' or 'not more than one malaria episode') were used in population- and family-based analyses. The strongest signal was observed for the interleukin 3 gene (IL3) SNP rs40401 (P = 3.4 × 10(-7), P(c)= 1.4 × 10(-4)). The IL3 genotypes rs40401(CT) and rs40401(TT) were found to exert a protective effect of 25% [incidence rate ratio (IRR) 0.75, P = 4.1 × 10(-5)] and 33% (IRR 0.67, P = 3.2 × 10(-8)), respectively, against malaria attacks. The association was confirmed in transmission disequilibrium tests (TDT, qTDT). The results could argue for a role of IL3 in the pathophysiology of falciparum malaria.
    Human Molecular Genetics 02/2011; 20(6):1173-81. · 7.69 Impact Factor
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    ABSTRACT: Recently, the World Health Organization emphasized the potential benefit of intermittent preventive treatment in infants (IPTi) to control malaria and officially recommended implementation of IPTi with sulfadoxine-pyrimethamine (SP) in areas with moderate and high transmission, where SP resistance is not high. As reported rebound effects make further observation mandatory, we performed a survey of participants of a former IPTi trial. Malariometric parameters were similar in the SP and the placebo group. In contrast, anti-Plasmodium falciparum lysate immunoglobulin G antibody levels, a proxy measure for preceding malaria episodes, remained lower in the SP arm. The most likely explanation is a lower overall exposure to parasitic antigens after IPTi.
    The Journal of Infectious Diseases 02/2011; 203(4):556-60. · 5.85 Impact Factor
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    ABSTRACT: Human parvovirus 4 has been considered to be transmitted only parenterally. However, after novel genotype 3 of parvovirus 4 was found in 2 patients with no parenteral risks, we tested infants in Ghana. A viremia rate of 8.6% over 2 years indicates that this infection is common in children in Africa.
    Emerging Infectious Diseases 07/2010; 16(7):1143-6. · 6.79 Impact Factor
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    ABSTRACT: The high prevalence of hemoglobin S (HbS) in Africa and hemoglobin C (HbC) in parts of West Africa is caused by the strong protection against severe falciparum malaria during childhood. Much less is known about the effect of HbS and especially HbC on Plasmodium falciparum infection, uncomplicated malaria, and anemia. A total of 1070 children from the Ashanti Region, Ghana, were enrolled at the age of 3 months and visited monthly until 2 years of age. The effects of the beta-globin genotype on the age-dependent incidence of malaria, levels of parasitemia, and hemoglobin as well as physical development were analyzed by population-averaged models. Infants with HbAS were protected from uncomplicated malaria (P < .005) and anemia (P < .001), had lower age-adjusted parasite densities (P < .001), and higher age-adjusted hemoglobin levels compared with children with the HbAA genotype (P = .004). In contrast, HbAC carriers had lower hemoglobin levels (P < .033) and were not protected against malaria or anemia. Notably, infants with HbAS were also significantly protected against stunting compared with carriers of HbAA or HbAC. This indicates differing mechanisms of protection against malaria of HbAS and HbAC and might help to understand why HbC is restricted to distinct areas of West Africa.
    Blood 03/2010; 115(22):4551-8. · 9.78 Impact Factor
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    ABSTRACT: Intermittent preventive treatment (IPT) is a promising strategy for malaria control in infants. We undertook a pooled analysis of the safety and efficacy of IPT in infants (IPTi) with sulfadoxine-pyrimethamine in Africa. We pooled data from six double-blind, randomised, placebo-controlled trials (undertaken one each in Tanzania, Mozambique, and Gabon, and three in Ghana) that assessed the efficacy of IPTi with sulfadoxine-pyrimethamine. In all trials, IPTi or placebo was given to infants at the time of routine vaccinations delivered by WHO's Expanded Program on Immunization. Data from the trials for incidence of clinical malaria, risk of anaemia (packed-cell volume <25% or haemoglobin <80 g/L), and incidence of hospital admissions and adverse events in infants up to 12 months of age were reanalysed by use of standard outcome definitions and time periods. Analysis was by modified intention to treat, including all infants who received at least one dose of IPTi or placebo. The six trials provided data for 7930 infants (IPTi, n=3958; placebo, n=3972). IPTi had a protective efficacy of 30.3% (95% CI 19.8-39.4, p<0.0001) against clinical malaria, 21.3% (8.2-32.5, p=0.002) against the risk of anaemia, 38.1% (12.5-56.2, p=0.007) against hospital admissions associated with malaria parasitaemia, and 22.9% (10.0-34.0, p=0.001) against all-cause hospital admissions. There were 56 deaths in the IPTi group compared with 53 in the placebo group (rate ratio 1.05, 95% CI 0.72-1.54, p=0.79). One death, judged as possibly related to IPTi because it occurred 19 days after a treatment dose, was subsequently attributed to probable sepsis. Four of 676 non-fatal hospital admissions in the IPTi group were deemed related to study treatment compared with five of 860 in the placebo group. None of three serious dermatological adverse events in the IPTi group were judged related to study treatment compared with one of 13 in the placebo group. IPTi with sulfadoxine-pyrimethamine was safe and efficacious across a range of malaria transmission settings, suggesting that this intervention is a useful contribution to malaria control. Bill & Melinda Gates Foundation.
    The Lancet 09/2009; 374(9700):1533-42. · 39.21 Impact Factor
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    ABSTRACT: While the protective effects of sickle cell trait (HbAS) against severe malaria and the resulting survival advantage are well known, the impact on the physical development in young children remains unclear. This study was aimed to investigate the relationship between HbS carriage and stunting in children below two years of age in a cohort from the Ashanti Region, Ghana. 1,070 children were recruited at three months of age and followed-up for 21 months with anthropometric measurements performed every three months. Incidence rate ratios with 95% confidence intervals were calculated by Poisson regression to estimate the association of beta-globin genotypes with the number of malaria episodes. Odds ratios (OR) were calculated for the association between the occurrence of beta-globin genotypes and/or malaria episodes and stunting. The age-dependent between-group and within-group effects for the beta-globin genotypes were assessed by population-averaged models estimated by generalized estimation equation with autoregressive correlation structure. Analyses showed a significantly lower age-dependent risk of stunting (OR 0.56; 95% CI 0.33-0.96) in carriers of the HbAS genotype (n = 102) in comparison to those with HbAA (n = 692). This effect was restricted to children who experienced malaria episodes during the observation period suggesting that the beneficial effect of the beta-globin HbS variant on the incidence of stunting is closely linked to its protection from mild malaria episodes. The lower risk of chronic malnutrition in early childhood, mediated by protection against mild malaria episodes, may contribute to the survival advantage of HbAS carriers in areas of high malaria transmission.
    Malaria Journal 02/2009; 8:16. · 3.49 Impact Factor
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    ABSTRACT: Numerous trials have demonstrated high efficacy and safety of artemisinin-based combination therapy (ACT) under supervised treatment. In contrast, effectiveness studies comparing different types of ACT applied unsupervised are scarce. The aim of this study was to compare effectiveness, tolerability and acceptance of artesunate plus amodiaquine (ASAQ) against that of artemether-lumefantrine (AL) in Ghanaian children with uncomplicated Plasmodium falciparum malaria. A randomized open-label trial was conducted at two district hospitals in the Ashanti region, Ghana, an area of intense malaria transmission. A total of 246 children under five years of age were randomly assigned to either ASAQ (Arsucam) or AL (Coartem). Study participants received their first weight-adjusted dose under supervision. After the parent/guardian was advised of times and mode of administration the respective three-day treatment course was completed unobserved at home. Follow-up visits were performed on days 3, 7, 14 and 28 to evaluate clinical and parasitological outcomes, adverse events, and haematological recovery. Length polymorphisms of variable regions of msp1 and msp2 were determined to differentiate recrudescences from reinfections. Acceptance levels of both treatment regimens were assessed by means of standardized interviews. Adequate clinical and parasitological responses after AL and ASAQ treatment were similar (88.3% and 91.7%, respectively). Interestingly, more late clinical failures until day 28 occurred in AL-treated children than in those who received ASAQ (17.5% and 7.3%, respectively; Hazard Ratio 2.41, 95% CI 1.00-5.79, p < 0.05).Haematological recovery and drug tolerability were not found to be significantly different in both study arms. The acceptance of treatment with ASAQ was higher than that with AL (rank-scores 10.6 and 10.3, respectively; p < 0.05). Unobserved AL and ASAQ treatment showed high adequate clinical and parasitological responses, though AL was inferior in preventing late clinical failures.
    Malaria Journal 12/2008; 7:261. · 3.49 Impact Factor
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    ABSTRACT: Intermittent preventive treatment in infants (IPTi) with sulphadoxine-pyrimethamine (SP) reduces the incidence of malaria episodes in young children. The exact mechanism by which the protective effect is mediated needs to be defined. This study aimed to investigate therapeutic, prophylactic, and possible exceeding effects of SP-based IPTi in two clinical trials. Protective efficacies from two IPTi trials performed in Kumasi, Ghana, and Lambaréné, Gabon, were assessed for overlapping time series of 61 days. For six-months periods after each of three IPTi doses a multivariate Poisson regression model with the respective cohort as co-variate was generated and effect modification of protective efficacy with time strata was evaluated by log-likelihood tests. Protective efficacies were not significantly different between the two study cohorts. Study-cohort corrected protective efficacy was highest for the first 61 days after each IPTi application and decreased continuously. For the first 61 days after IPTi-1, IPTi-2, and IPTi-3 the protective efficacy was 71%, 44%, and 43%, respectively. A reduction of the malaria incidence rate was detectable for the first 60, 30 and 40 days after IPTi-1, IPTi-2 and IPTi-3 drug application, respectively. After IPTi-3 a higher risk for malaria could be seen after day 60. This effect was mainly based on the overwhelming influence of the Kumasi cohort. The results suggest that SP-based IPTi mainly works through a therapeutic and prophylactic effect over 30 to 60 days after drug application and that a sustained effect beyond post-treatment prophylaxis might be very low. Data analysis from clinical trials NCT ID # 00206739 (Kumasi Trial) and NCT ID # 00167843 (Lambaréné Trial), http://www.clinicaltrials.gov.
    Malaria Journal 11/2008; 7:198. · 3.49 Impact Factor
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    Emerging infectious diseases 03/2008; 14(2):344-6. · 5.99 Impact Factor
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    ABSTRACT: Clinical immunity to Plasmodium falciparum malaria develops after repeated exposure to the parasite. At least 2 P. falciparum variant antigens encoded by multicopy gene families (var and rif) are targets of this adaptive antibody-mediated immunity. A third multigene family of variant antigens comprises the stevor genes. Here, 4 different stevor sequences were selected for cloning and expression in Escherichia coli and His6-tagged fusion proteins were used for assessing the development of immunity. In a cross-sectional analysis of clinically immune adults living in a malaria endemic area in Ghana, high levels of anti-STEVOR IgG antibody titres were determined in ELISA. A cross-sectional study of 90 nine-month-old Ghanaian infants using 1 recombinant STEVOR showed that the antibody responses correlated positively with the number of parasitaemia episodes. In a longitudinal investigation of 17 immunologically naïve 9-month-old infants, 3 different patterns of anti-STEVOR antibody responses could be distinguished (high, transient and low). Children with high anti-STEVOR-antibody levels exhibited an elevated risk for developing parasitaemia episodes. Overall, a protective effect could not be attributed to antibodies against the STEVOR proteins chosen for the study presented here.
    Parasitology 03/2008; 135(2):155-67. · 2.36 Impact Factor
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    ABSTRACT: In sub-Saharan Africa, malaria is a leading cause of morbidity and mortality among young children. Detailed knowledge of spatial variation of malaria epidemiology and associated risk factors is important for planning and evaluating malaria-control measures. The spatial variation of malaria incidences and socioeconomic factors were assessed over 21 months, from January 2003 to September 2005, in 535 children from 9 villages of a small rural area with high Plasmodium falciparum transmission in Ghana. Household positions were mapped by use of a global positioning system, and the spatial effects on malaria rates were assessed by means of ecological analyses and bivariate Poisson regression controlling for possible confounding factors. Malaria incidence was surprisingly heterogeneous between villages, and ecological analyses showed strong correlations with village area (R(2) = 0.74; P = .003) and population size (R(2) = 0.68; P = .006). Malaria risk was affected by a number of socioeconomic factors. Poisson regression showed an independent linear rate reduction with increasing distance between children's households and the fringe of the forest. The exact location of households in villages is an independent and important factor for the variation of malaria incidence in children from high-transmission areas. This fact should be considered in the planning of intervention trials and in spatial targeting of malaria interventions at a local level.
    The Journal of Infectious Diseases 02/2008; 197(1):85-93. · 5.85 Impact Factor
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    ABSTRACT: To assess how intermittent preventive treatment in infants (IPTi) with sulphadoxine-pyrimethamine (SP) affects Immunoglobulin (IgG) immune responses against Plasmodium falciparum in infants from rural Ghana. Randomized, placebo-controlled and double-blinded clinical trial with participants randomized in blocks of 10 to receive either 250 mg sulphadoxine/2.5 mg pyrimethamine or placebo at the age of 3 (IPTi-1), 9 (IPTi-2) and 15 (IPTi-3) months and followed-up for 21 months. (i) Anti-P. falciparum IgG levels were measured in 180 children at the age of 9 months. (ii) Longitudinal study of the relationship between IgG levels and P. falciparum infections and/or clinical malaria in 17 naive children until they reached the age of 2 years. IgG antibody levels against crude P. falciparum lysate were dependent on the frequency of preceding infections and significantly lower in children treated with SP. Placebo-treated children had an indifferentially higher incidence of P. falciparum infections than clinically observed, which implicates an underestimation of the protective efficacy of IPTi. IgG profiles in 17 children followed up until the age of 2 years provided no evidence for impaired immune responses after a single dose of SP within the framework of IPTi.
    Tropical Medicine & International Health 11/2007; 12(10):1157-63. · 2.94 Impact Factor
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    ABSTRACT: Intermittent preventive antimalarial treatment in infants (IPTi) with sulfadoxine-pyrimethamine reduces falciparum malaria and anemia but has not been evaluated in areas with intense perennial malaria transmission. It is unknown whether an additional treatment in the second year of life prolongs protection. A randomized, double-blinded, placebo-controlled trial with administration of sulfadoxine-pyrimethamine therapy at 3, 9, and 15 months of age was conducted with 1070 children in an area in Ghana where malaria is holoendemic. Participants were monitored for 21 months after recruitment through active follow-up visits and passive case detection. The primary end point was malaria incidence, and additional outcome measures were anemia, outpatient visits, hospital admissions, and mortality. Stratified analyses for 6-month periods after each treatment were performed. Protective efficacy against malaria episodes was 20% (95% confidence interval [CI], 11%-29%). The frequency of malaria episodes was reduced after the first 2 sulfadoxine-pyrimethamine applications (protective efficacy, 23% [95% CI, 6%-36%] after the first dose and 17% [95% CI, 1%-30%] after the second dose). After the third treatment at month 15, however, no protection was achieved. Protection against the first or single anemia episode was only significant after the first IPTi dose (protective efficacy, 30%; 95% CI, 5%-49%). The number of anemia episodes increased after the last IPTi dose (protective efficacy, -24%; 95% CI, -50% to -2%). In an area of intense perennial malaria transmission, sulfadoxine-pyrimethamine-based IPTi conferred considerably lower protection than reported in areas where the disease is moderately or seasonally endemic. Protective efficacy is age-dependent, and extension of IPTi into the second year of life does not provide any benefit.
    Clinical Infectious Diseases 08/2007; 45(1):16-25. · 9.37 Impact Factor
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    ABSTRACT: Intermittent preventive antimalarial treatment in infants (IPTi) is currently evaluated as a malaria control strategy. Among the factors influencing the extent of protection that is provided by IPTi are the transmission intensity, seasonality, drug resistance patterns, and the schedule of IPTi administrations. The aim of this study was to determine how far the protective efficacy of IPTi depends on spatio-temporal variations of the prevailing incidence of malaria. One thousand seventy infants were enrolled in a registered controlled trial on the efficacy of IPTi with sulphadoxine-pyrimethamine (SP) in the Ashanti Region, Ghana, West Africa (ClinicalTrial.gov: NCT00206739). Stratification for the village of residence and the month of birth of study participants demonstrated that the malaria incidence was dependent on spatial (range of incidence rates in different villages 0.6-2.0 episodes/year) and temporal (range of incidence rates in children of different birth months 0.8-1.2 episodes/year) factors. The range of spatio-temporal variation allowed ecological analyses of the correlation between malaria incidence rates, anti-Plasmodium falciparum lysate IgG antibody levels and protective efficacies provided by IPTi. Protective efficacy of the first SP administration was positively correlated with malaria incidences in children living in a distinct village or born in a distinct month (R2 0.48, p < 0.04 and R2 0.63, p < 0.003, respectively). Corresponding trends were seen after the second and third study drug administration. Accordingly, IgG levels against parasite lysate increased with malaria incidence. This correlation was stronger in children who received IPTi, indicating an effect modification of the intervention. The spatial and temporal variations of malaria incidences in a geographically and meteorologically homogeneous study area exemplify the need for close monitoring of local incidence rates in all types of intervention studies. The increase of the protective efficacy of IPTi with malaria incidences may be relevant for IPTi implementation strategies and, possibly, for other malaria control measures.
    Malaria Journal 02/2007; 6:163. · 3.49 Impact Factor
  • International Journal of Antimicrobial Agents - INT J ANTIMICROBIAL AGENTS. 01/2007; 29.
  • R. Kobbe, S. Adjei, O. Adjei, J. May
    International Journal of Antimicrobial Agents - INT J ANTIMICROBIAL AGENTS. 01/2007; 29.
  • International Journal of Antimicrobial Agents - INT J ANTIMICROBIAL AGENTS. 01/2007; 29.
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    ABSTRACT: To assess the prevalence and multiplicity of Plasmodium falciparum infections in Ghanaian infants. In an epidemiological study in an area holoendemic for malaria in Ghana, the prevalence and multiplicity of P. falciparum infections (MOI) were assessed in 1069 three month-old infants by typing of the genes encoding the merozoite surface proteins 1 and 2 (msp-1, msp-2) over a recruitment period of one year. Alleles were amplified using allele family-specific polymerase chain reaction (PCR) assays and determined according to their length polymorphisms on a genetic analyzer. The occurrence of early infections was dependent on the season (month-stratified prevalence 6.4-29.0%). Diversity of msp-alleles was extensive and significantly higher in the dry than in the rainy season. The level of infection prevalence and the high multiplicity of infections (median 4, maximum 14 strains per isolate) in the first months of life indicate early contacts with parasites exhibiting a wide repertoire of antigens and, most likely, multiple infections per single mosquito bite.
    Tropical Medicine & International Health 06/2006; 11(5):613-9. · 2.94 Impact Factor

Publication Stats

643 Citations
227.41 Total Impact Points

Institutions

  • 2006–2011
    • Bernhard Nocht Institute for Tropical Medicine
      • Research Group Infectious Disease Epidemiology
      Hamburg, Hamburg, Germany
  • 2009
    • University Medical Center Hamburg - Eppendorf
      Hamburg, Hamburg, Germany
    • Ghana Health Service
      Akra, Greater Accra, Ghana
  • 2008
    • Kumasi Centre for Collaborative Research in Tropical Medicine
      Coomassie, Ashanti, Ghana