Lassa Virus Countermeasures

Safety, immunogenicity, efficacy, and effectiveness of Lassa fever vaccines in pregnant persons, children, and adolescents: a protocol for a living systematic review and meta-analysis

BACKGROUND

Lassa fever (LF), caused by the Lassa virus (LASV), is a zoonotic viral hemorrhagic disease endemic to West Africa, primarily transmitted through rodent excreta and infected bodily fluids. It poses significant public health challenges due to its high morbidity and mortality rates, particularly among at-risk populations like pregnant persons and children. Despite decades of research, vaccine development has been hindered by the virus's genetic diversity and complex epidemiology. While several vaccine candidates have been developed, none have received regulatory approval. Given the rapidly evolving vaccine landscape, a living systematic review (LSR) was selected to enable real-time evidence synthesis. This protocol outlines a living systematic review (LSR) to evaluate the safety, efficacy, effectiveness, and immunogenicity of LASV vaccines, providing evidence to guide public health interventions and vaccine recommendations.

METHODS

We will conduct a biweekly updated LSR and meta-analysis, systematically searching databases (e.g., MEDLINE, EMBASE, CENTRAL) and clinical trial registries from January 2014 onward to identify studies of LASV vaccines in pregnant persons, children, and adolescents. All study designs, including randomized trials, cohort studies, case-control studies, and case reports, will be eligible. Pairs of reviewers will independently assess eligibility, extract data, and evaluate the risk of bias. Primary outcomes include vaccine safety, efficacy, and effectiveness in pregnant persons (including neonatal outcomes), children, and adolescents, while secondary outcomes assess immunogenicity and reactogenicity. Data on adult populations will also be included, and results on this group will be reported as available. We will conduct paired meta-analyses, including prespecified subgroup and sensitivity analyses. We will use the grading of recommendations assessment, development, and evaluation approach to evaluate the certainty of evidence.

DISCUSSION

This LSR offers a dynamic framework to generate timely evidence on LASV vaccines for vulnerable populations. By integrating findings into an interactive Microsoft Power BI dashboard, stakeholders can access and utilize real-time updates to inform public health strategies. Despite challenges like study heterogeneity and vaccine platform variability, subgroup and sensitivity analyses will mitigate these issues. This review aims to support clinical trial designs, guide policy, and improve health outcomes in Lassa fever-endemic regions.

STUDY REGISTRATION

Two protocols were registered in the International Prospective Register of Systematic Reviews (PROSPERO) database: CRD42024514513 and CRD42024516754.

Lassa Fever Natural History and Clinical Management

Lassa fever is caused by Lassa virus (LASV), an Old World Mammarenavirus that is carried by Mastomys natalensis and other rodents. It is endemic in Sierra Leone, Nigeria, and other countries in West Africa. The clinical presentation of LASV infection is heterogenous varying from an inapparent or mild illness to a fatal hemorrhagic fever. Exposure to LASV is usually through contact with rodent excreta. After an incubation period of 1-3 weeks, initial symptoms such as fever, headache, and fatigue develop that may progress to sore throat, retrosternal chest pain, conjunctival injection, vomiting, diarrhea, and abdominal pain. Severe illness, including hypotension, shock, and multiorgan failure, develops in a minority of patients. Patient demographics and case fatality rates are distinctly different in Sierra Leone and Nigeria. Laboratory diagnosis relies on the detection of LASV antigens or genomic RNA. LASV-specific immunoglobulin G and M assays can also contribute to clinical management. The mainstay of treatment for Lassa fever is supportive care. The nucleoside analog ribavirin is commonly used to treat acute Lassa fever but is considered useful only if treatment is begun early in the disease course. Drugs in development, including a monoclonal antibody cocktail, have the potential to impact the management of Lassa fever.

Lassa Virus Structural Biology and Replication

Lassa virus (LASV) is the causative agent of Lassa fever, an often-fatal hemorrhagic fever that is endemic in West Africa. LASV virions are enveloped and contain two single-stranded RNA genome segments. Both segments are ambisense and encode two proteins. The nucleoprotein associates with viral RNAs forming ribonucleoprotein complexes. The glycoprotein complex mediates viral attachment and entry. The Zinc protein serves as the matrix protein. Large is a polymerase that catalyzes viral RNA transcription and replication. LASV virion entry occurs via a clathrin-independent endocytic pathway usually involving alpha-dystroglycan and lysosomal associated membrane protein 1 as surface and intracellular receptors, respectively. Advances in understanding LASV structural biology and replication have facilitated development of promising vaccine and drug candidates.