Towards an effective malaria vaccine

Global prevalence and determinants associated with the acceptance of monkeypox vaccination

Assessing the acceptance of the monkeypox vaccine is crucial for the success of vaccination programs, yet the prevalence reports remain inconclusive. The aim of this study was to determine the global prevalence of monkeypox vaccine acceptance and identify its associated factors. A meta-analysis was conducted with a comprehensive search strategy on the following databases, including Scopus, Embase, and PubMed, for articles published up to April 5, 2024. This study utilizes a single-arm meta-analysis to calculate the pooled prevalence of monkeypox vaccine acceptance. A Z-test was employed to identify factors associated with the vaccine acceptance. Our study analyzed 51 articles encompassing 98,746 participants, revealing an overall monkeypox vaccine acceptance rate of 65%. Notably, the highest acceptance rates were observed among men who have sex with men (MSMs), while healthcare workers (HCWs) showed the lowest acceptance rates. Additionally, our findings indicated an increased acceptance in individuals with educational attainment beyond a bachelor's degree, a history of COVID-19 and influenza vaccination, homosexual orientation, and HIV-positive status. Conversely, lower acceptance risk was associated with those with educational attainment below a bachelor's degree, heterosexual orientation, and bisexual orientation. In conclusion, our current study has determined the rate of monkeypox vaccine acceptance and identified its associated factors. These findings offer valuable insights as the foundation for targeted policies to manage and increase acceptance rates.

Global Prevalence and Potential Influencing Factors of COVID-19 Vaccination Hesitancy: A Meta-Analysis

Countries worldwide have deployed mass COVID-19 vaccination drives, but there are people who are hesitant to receive the vaccine. Studies assessing the factors associated with COVID-19 vaccination hesitancy are inconclusive. This study aimed to assess the global prevalence of COVID-19 vaccination hesitancy and determine the potential factors associated with such hesitancy. We performed an organized search for relevant articles in PubMed, Scopus, and Web of Science. Extraction of the required information was performed for each study. A single-arm meta-analysis was performed to determine the global prevalence of COVID-19 vaccination hesitancy; the potential factors related to vaccine hesitancy were analyzed using a Z-test. A total of 56 articles were included in our analysis. We found that the global prevalence of COVID-19 vaccination hesitancy was 25%. Being a woman, being a 50-year-old or younger, being single, being unemployed, living in a household with five or more individuals, having an educational attainment lower than an undergraduate degree, having a non-healthcare-related job and considering COVID-19 vaccines to be unsafe were associated with a higher risk of vaccination hesitancy. In contrast, living with children at home, maintaining physical distancing norms, having ever tested for COVID-19, and having a history of influenza vaccination in the past few years were associated with a lower risk of hesitancy to COVID-19 vaccination. Our study provides valuable information on COVID-19 vaccination hesitancy, and we recommend special interventions in the sub-populations with increased risk to reduce COVID-19 vaccine hesitancy.

Pre-Erythrocytic Vaccines against Malaria

Malaria, caused by the protozoan Plasmodium, is a devastating disease with over 200 million new cases reported globally every year. Although immunization is arguably the best strategy to eliminate malaria, despite decades of research in this area we do not have an effective, clinically approved antimalarial vaccine. The current impetus in the field is to develop vaccines directed at the pre-erythrocytic developmental stages of Plasmodium, utilizing novel vaccination platforms. We here review the most promising pre-erythrocytic stage antimalarial vaccine candidates.

Malaria endemicity and co-infection with tissue-dwelling parasites in Sub-Saharan Africa: a review

Mechanisms and outcomes of host-parasite interactions during malaria co-infections with gastrointestinal helminths are reasonably understood. In contrast, very little is known about such mechanisms in cases of malaria co-infections with tissue-dwelling parasites. This is lack of knowledge is exacerbated by misdiagnosis, lack of pathognomonic clinical signs and the chronic nature of tissue-dwelling helminthic infections. A good understanding of the implications of tissue-dwelling parasitic co-infections with malaria will contribute towards the improvement of the control and management of such co-infections in endemic areas. This review summarises and discusses current information available and gaps in research on malaria co-infection with gastro-intestinal helminths and tissue-dwelling parasites with emphasis on helminthic infections, in terms of the effects of migrating larval stages and intra and extracellular localisations of protozoan parasites and helminths in organs, tissues, and vascular and lymphatic circulations.

Oral delivery of human biopharmaceuticals, autoantigens and vaccine antigens bioencapsulated in plant cells

Among 12billion injections administered annually, unsafe delivery leads to >20million infections and >100million reactions. In an emerging new concept, freeze-dried plant cells (lettuce) expressing vaccine antigens/biopharmaceuticals are protected in the stomach from acids/enzymes but are released to the immune or blood circulatory system when plant cell walls are digested by microbes that colonize the gut. Vaccine antigens bioencapsulated in plant cells upon oral delivery after priming, conferred both mucosal and systemic immunity and protection against bacterial, viral or protozoan pathogens or toxin challenge. Oral delivery of autoantigens was effective against complications of type 1 diabetes and hemophilia, by developing tolerance. Oral delivery of proinsulin or exendin-4 expressed in plant cells regulated blood glucose levels similar to injections. Therefore, this new platform offers a low cost alternative to deliver different therapeutic proteins to combat infectious or inherited diseases by eliminating inactivated pathogens, expensive purification, cold storage/transportation and sterile injections.

Histopathological effects of sub-chronic lamivudine-artesunate co-administration on the liver of diseased adult Wistar rats

Background:

Lamivudine and artesunate are sometimes co administered in HIV-malaria co morbidity. Both drugs are used concurrently in presumptive malaria treatment and simultaneous HIV post exposure prophylaxis.

Aim:

The aim of this study was to investigate the effect of lamivudine-artesunate co administration on the histology of the liver of diseased adult Wistar rats.

Materials and Methods:

Five groups of rats of both sexes were used for the study and placed on feed and water ad libitum. Disease state consisted of immunosuppression with cyclophosphamide, and infection with Plasmodium berghei. Group 1 animals served as vehicle control, while group 2 were the diseased controls. Group 3 animals received 20 mg/kg lamivudine for three weeks, while group 4 similarly received 20 mg/kg Lamivudine but also received 10 mg/kg artesunate from day 12. Animals in group 5 received 10 mg/kg artesunate from day 12. All drugs were administered intraperitoneally. The animals were treated for twenty-one days, at the end of which they were sacrificed and their livers fixed in 10% formalin for histological studies.

Result:

Results from the study show the presence of regions of focal necrosis and perivascular cuffing with animals that received artesunate. Hemosiderosis was a common feature in all the parasitized groups, while fatty degeneration was observed in the group that received artesunate alone.

Conclusion:

Concurrent lamivudine-artesunate administration resulted in some histopathological changes in the liver. This study suggests there may be considerable histological changes with repeated occurrence of malaria and immunosuppression that may warrant intermittent lamivudine-artesunate administration, and may require evaluation as well as monitoring of liver function during such therapeutic interventions.

Approaching the target: the path towards an effective malaria vaccine

Developing an effective malaria vaccine has been the goal of the scientific community for many years. A malaria vaccine, added to existing tools and strategies, would further prevent infection and decrease the unacceptable malaria morbidity and mortality burden. Great progress has been made over the last decade and a number of vaccine candidates are in the clinical phases of development. The RTS,S malaria vaccine candidate, based on a recombinant P. falciparum protein, is the most advanced of such candidates, currently undergoing a large phase III trial. RTS,S has consistently shown around 50% efficacy protecting against the first clinical episode of malaria, in some cases extending up to 4 years. It is hoped that RTS,S will eventually become the first licensed malaria vaccine. This first vaccine against a human parasite is a groundbreaking achievement, but improved malaria vaccines conferring higher protection will be needed if the aspiration of malaria eradication is to be achieved.

Generation of humoral immune responses to multi-allele PfAMA1 vaccines; effect of adjuvant and number of component alleles on the breadth of response

There is increasing interest in multi-allele vaccines to overcome strain-specificity against polymorphic vaccine targets such as Apical Membrane Antigen 1 (AMA1). These have been shown to induce broad inhibitory antibodies in vitro and formed the basis for the design of three Diversity-Covering (DiCo) proteins with similar immunological effects. The antibodies produced are to epitopes that are shared between vaccine alleles and theoretically, increasing the number of component AMA1 alleles is expected to broaden the antibody response. A plateau effect could however impose a limit on the number of alleles needed to achieve the broadest specificity. Moreover, production cost and the vaccine formulation process would limit the number of component alleles. In this paper, we compare rabbit antibody responses elicited with multi-allele vaccines incorporating seven (three DiCos and four natural AMA1 alleles) and three (DiCo mix) antigens for gains in broadened specificity. We also investigate the effect of three adjuvant platforms on antigen specificity and antibody functionality. Our data confirms a broadened response after immunisation with DiCo mix in all three adjuvants. Higher antibody titres were elicited with either CoVaccine HT™ or Montanide ISA 51, resulting in similar in vitro inhibition (65–82%) of five out of six culture-adapted P. falciparum strains. The antigen binding specificities of elicited antibodies were also similar and independent of the adjuvant used or the number of vaccine component alleles. Thus neither the four extra antigens nor adjuvant had any observable benefits with respect to specificity broadening, although adjuvant choice influenced the absolute antibody levels and thus the extent of parasite inhibition. Our data confirms the feasibility and potential of multi-allele PfAMA1 formulations, and highlights the need for adjuvants with improved antibody potentiation properties for AMA1-based vaccines.

Chloroplast-derived vaccine antigens confer dual immunity against cholera and malaria by oral or injectable delivery

Cholera and malaria are major diseases causing high mortality. The only licensed cholera vaccine is expensive; immunity is lost in children within 3 years and adults are not fully protected. No vaccine is yet available for malaria. Therefore, in this study, the cholera toxin-B subunit (CTB) of Vibrio cholerae fused to malarial vaccine antigens apical membrane antigen-1 (AMA1) and merozoite surface protein-1 (MSP1) was expressed in lettuce and tobacco chloroplasts. Southern blot analysis confirmed homoplasmy and stable integration of transgenes. CTB-AMA1 and CTB-MSP1 fusion proteins accumulated up to 13.17% and 10.11% (total soluble protein, TSP) in tobacco and up to 7.3% and 6.1% (TSP) in lettuce, respectively. Nine groups of mice (n = 10/group) were immunized subcutaneously (SQV) or orally (ORV) with purified antigens or transplastomic tobacco leaves. Significant levels of antigen-specific antibody titres of immunized mice completely inhibited proliferation of the malarial parasite and cross-reacted with the native parasite proteins in immunoblots and immunofluorescence studies. Protection against cholera toxin challenge in both ORV (100%) and SQV (89%) mice correlated with CTB-specific titres of intestinal, serum IgA and IgG1 in ORV and only IgG1 in SQV mice, but no other immunoglobulin. Increasing numbers of interleukin-10(+) T cell but not Foxp3(+) regulatory T cells, suppression of interferon-gamma and absence of interleukin-17 were observed in protected mice, suggesting that immunity is conferred via the Tr1/Th2 immune response. Dual immunity against two major infectious diseases provided by chloroplast-derived vaccine antigens for long-term (>300 days, 50% of mouse life span) offers a realistic platform for low cost vaccines and insight into mucosal and systemic immunity.

Vaccinating with the genome: a Sisyphean task?

Human trials of subunit vaccines against the asexual blood stage of malaria are yielding disappointing results, supporting the premise that a single recombinant protein will not be particularly efficacious and that additional proteins must be added. The genome sequence of Plasmodium falciparum offers a large number of additional candidates, but which should be chosen? Various criteria have been suggested to rank the additional candidates, but in the absence of even a partially effective asexual-stage vaccine, the criteria remain unvalidated. These issues are discussed here, together with some suggestions as to how the development of an asexual-stage vaccine could be progressed.

Estimation of vaccine efficacy in a repeated measures study under heterogeneity of exposure or susceptibility to infection

Vaccine efficacy (VE) is commonly estimated through proportional hazards modelling of the time to first infection or disease, even when the event of interest can recur. These methods can result in biased estimates when VE is heterogeneous across levels of exposure and susceptibility in subjects. These two factors are important sources of unmeasured heterogeneity, since they vary within and across areas, and often cannot be individually quantified. We propose an estimator of VE per exposure that accounts for heterogeneous susceptibility and exposure for a repeated measures study with binary recurrent outcomes. The estimator requires only information about the probability distribution of environmental exposures. Through simulation studies, we compare the properties of this estimator with proportional hazards estimation under the heterogeneity of exposure. The methods are applied to a reanalysis of a malaria vaccine trial in Brazil.

Import of malaria in a Romanian Western County

BACKGROUND

Malaria is not a serious concern in Romania nowadays although 30-60 imported cases are diagnosed yearly, especially in travellers from Africa. Timis, the most extensive of the Romanian counties, is the western gate of the country from where a lot of people travel abroad. The aim of this study is to overview all the imported cases of malaria diagnosed in our county and to describe two recent severe cases.

METHODS

We retrospectively analyzed both the medical records of 28 malaria patients treated between 1974 and 2007 at Victor Babes Hospital of Infectious Disease from Timisoara, Romania, and the results of 6 blood examinations performed in the last decade in the parasitological laboratory of Victor Babes University of Medicine and Pharmacy from Timisoara. A comparison between the two recent severe cases was made, emphasizing on the clinical aspects, complications and the laboratory test results.

RESULTS

Most of the patients (55.38%) were in the age group of 20-29 years; 85.71% of the patients were males; Plasmodium falciparum was found in 75% of the cases.

CONCLUSIONS

Findings of our study have shown that P. falciparum is the main malaria species in Timis County, outlining the difficulties in the diagnosis and management of the imported cases.

Malaria drug and vaccine trials in Africa: obstacles and opportunities

There are several new treatments and vaccine technologies in clinical development for childhood malaria that have arrived in the clinical phase of evaluation during the past 5-10 years. This is a long-awaited change as until this time there had been little in the pipeline. As these products progress, evaluating them in the populations for whom they are being developed is becoming increasingly challenging. Many more capable trial sites are required and thousands of children and their parents need to be willing to take part in all the clinical trials that will be necessary if even a handful of these products make it through to obtaining a marketing approval license. Then, beyond licensure, these products will need to be assessed in more 'real-life' phase IV trials to establish whether they can truly impact the high level of mortality that malaria brings to the under-five population in Africa. Here we explore the issues that face both the trial sites and the product developers and present how this opportunity should be utilised to develop experienced African clinical researchers and facilities alongside getting these products through into public health use.