Malaria vaccine trial endpoints - bridging the gaps between trial design, public health and the next generation of vaccines

Semiparametric estimation of time-varying intervention effects using recurrent event data

We consider the estimation of the optimal interval between doses for interventions such as malaria chemoprevention and vaccine booster doses that are applied intermittently in infectious disease control. A flexible exponential-like function to model the time-varying intervention effect in the framework of Andersen-Gill model for recurrent event time data is considered. The partial likelihood estimation approach is adopted, and a large scale simulation study is carried out to evaluate the performance of the proposed method. A simple guideline for the choice of the optimal interval between successive doses is proposed. The methodology is illustrated with the analysis of data from a malaria chemoprevention trial. Copyright © 2017 John Wiley & Sons, Ltd.

Oxidative stress and genes regulation of cerebral malaria upon Zizyphus spina-christi treatment in a murine model

The development and spread of multidrug-resistant strains of malarial parasites have led to an overwhelming increase in the resistance to current antimalarial drugs. The urgent need for alternative antimalarial drugs has directed some of the current studies toward folkloric medicine approaches. Interestingly, the Zizyphus spina Cristi leaf extract (ZLE) has been found to exhibit antiplasmodial activity. This study evaluated the protective effect of ZLE against Plasmodium berghei-induced cerebral tissue injuries in mice. Male C57Bl/6 mice received an injection of P. berghei-infected red blood cells. Mice were divided into three groups (control, infected, and ZLE-treated), and were subjected to histological, biochemical, and molecular analyses. Murine malaria infections induced significant weight loss; however, upon ZLE treatment, the weight of mice was markedly restored. Additionally, infected mice showed brain histopathological changes and induction of oxidative damage. Significantly, ZLE treatment restored the levels of oxidative markers and antioxidant enzyme to the normal ranges. The mRNA expression of several genes in the brain of mice including Cacnb4, Adam23, Glrb, Vdac3, and Cabp1 was significantly upregulated during P. berghei infection. In contrast, ZLE markedly reduced the mRNA expression of these genes. To conclude, the results indicate that ZLE could play an important role in reducing the destructive effect of P. berghei-induced cerebral malaria owing to its antiplasmodial and antioxidant activities.

High prevalence of malaria parasitemia and anemia among hospitalized children in Rakai, Uganda

Background

There is a paucity of data on malaria among hospitalized children in malaria endemic areas. We determined the prevalence, presentation and treatment outcomes of malaria and anemia among children in two hospitals in Rakai, Uganda.

Methods

Children under five years hospitalized in Kalisizo hospital or Bikira health center in Rakai district, Uganda between May 2011 and May 2012 were enrolled and followed-up until discharge, death or referral. Data were collected on social-demographic characteristics, current and past illnesses and clinical signs and symptoms. Blood smears, hemoglobin (Hgb) levels and HIV testing were performed from finger/heel prick blood. The associations between malaria infection and other factors were estimated using log-binomial regression to estimate adjusted prevalence risk ratios (aPRR) and 95% confidence intervals (CIs), controlling for clustering at health facilities.

Results

2471 children were enrolled. The most common medical presentations were fever (96.2%), cough (61.7%), vomiting (44.2%), diarrhea (20.8%), and seizures (16.0%). The prevalence of malaria parasitemia was 54.6%. Children with malaria were more likely to present with a history of fever (aPRR 2.23; CI 1.18–4.24) and seizures (aPRR 1.12; CI 1.09–1.16). Confirmed malaria was significantly lower among girls than boys (aPRR 0.92; CI 0.91–0.93), HIV infected children (aPRR 0.60 CI 0.52–0.71), and children with diarrhea (aPRR 0.76; CI 0.65–0.90). The overall prevalence of anemia (Hgb<10 g/dl) was 56.3% and severe anemia (Hgb<6 g/dL) was 17.8%. Among children with severe anemia 76.8% had malaria parasitemia, of whom 93.1% received blood transfusion. Malaria associated mortality was 0.6%.

Conclusion

There was a high prevalence of malaria parasitemia and anemia among inpatient children under five years. Malaria prevention is a priority in this population.

Effect of supplementation with zinc and other micronutrients on malaria in Tanzanian children: a randomised trial

BACKGROUND

It is uncertain to what extent oral supplementation with zinc can reduce episodes of malaria in endemic areas. Protection may depend on other nutrients. We measured the effect of supplementation with zinc and other nutrients on malaria rates.

METHODS AND FINDINGS

In a 2×2 factorial trial, 612 rural Tanzanian children aged 6-60 months in an area with intense malaria transmission and with height-for-age z-score≤-1.5 SD were randomized to receive daily oral supplementation with either zinc alone (10 mg), multi-nutrients without zinc, multi-nutrients with zinc, or placebo. Intervention group was indicated by colour code, but neither participants, researchers, nor field staff knew who received what intervention. Those with Plasmodium infection at baseline were treated with artemether-lumefantrine. The primary outcome, an episode of malaria, was assessed among children reported sick at a primary care clinic, and pre-defined as current Plasmodium infection with an inflammatory response, shown by axillary temperature ≥37.5°C or whole blood C-reactive protein concentration ≥ 8 mg/L. Nutritional indicators were assessed at baseline and at 251 days (median; 95% reference range: 191-296 days). In the primary intention-to-treat analysis, we adjusted for pre-specified baseline factors, using Cox regression models that accounted for multiple episodes per child. 592 children completed the study. The primary analysis included 1,572 malaria episodes during 526 child-years of observation (median follow-up: 331 days). Malaria incidence in groups receiving zinc, multi-nutrients without zinc, multi-nutrients with zinc and placebo was 2.89/child-year, 2.95/child-year, 3.26/child-year, and 2.87/child-year, respectively. There was no evidence that multi-nutrients influenced the effect of zinc (or vice versa). Neither zinc nor multi-nutrients influenced malaria rates (marginal analysis; adjusted HR, 95% CI: 1.04, 0.93-1.18 and 1.10, 0.97-1.24 respectively). The prevalence of zinc deficiency (plasma zinc concentration <9.9 µmol/L) was high at baseline (67% overall; 60% in those without inflammation) and strongly reduced by zinc supplementation.

CONCLUSIONS

We found no evidence from this trial that zinc supplementation protected against malaria.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00623857

Statistical methodology for the evaluation of vaccine efficacy in a phase III multi-centre trial of the RTS, S/AS01 malaria vaccine in African children

Background

There has been much debate about the appropriate statistical methodology for the evaluation of malaria field studies and the challenges in interpreting data arising from these trials.

Methods

The present paper describes, for a pivotal phase III efficacy of the RTS, S/AS01 malaria vaccine, the methods of the statistical analysis and the rationale for their selection. The methods used to estimate efficacy of the primary course of vaccination, and of a booster dose, in preventing clinical episodes of uncomplicated and severe malaria, and to determine the duration of protection, are described. The interpretation of various measures of efficacy in terms of the potential public health impact of the vaccine is discussed.

Conclusions

The methodology selected to analyse the clinical trial must be scientifically sound, acceptable to regulatory authorities and meaningful to those responsible for malaria control and public health policy.

Trial registration

Clinicaltrials.gov NCT00866619

Heterogeneity in malaria exposure and vaccine response: implications for the interpretation of vaccine efficacy trials

Background

Phase III trials of the malaria vaccine, RTS, S, are now underway across multiple sites of varying transmission intensity in Africa. Heterogeneity in exposure, vaccine response and waning of efficacy may bias estimates of vaccine efficacy.

Methods

Theoretical arguments are used to identify the expected effects of a) heterogeneity in exposure to infectious bites; b) heterogeneity in individual's response to the vaccine; and c) waning efficacy on measures of vaccine efficacy from clinical trials for an infection-blocking vaccine.

Results

Heterogeneity in exposure and vaccine response leads to a smaller proportion of trial participants becoming infected than one would expect in a homogeneous setting. This causes estimates of vaccine efficacy from clinical trials to be underestimated if transmission heterogeneity is ignored, and overestimated if heterogeneity in vaccine response is ignored. Waning of vaccine efficacy can bias estimates of vaccine efficacy in both directions.

Conclusions

Failure to account for heterogeneities in exposure and response, and waning of efficacy in clinical trials can lead to biased estimates of malaria vaccine efficacy. Appropriate methods to reduce these biases need to be used to ensure accurate interpretation and comparability between trial sites of results from the upcoming Phase III clinical trials of RTS, S.