YFV 17D C- PrM-E genes were amplified from pACNR-FLYFV17DII and cloned as BamHI- and XhoI-digested fragments into a likewise pcDNA3.1-digested plasmid (Invitrogen, Thermo Fisher Scientific, Waltham, MA) [19]. The second plasmid WNVVII reporterCGFP, containing the NS1-NS2-NS3-NS4-NS5 region from the lineage II strain of West Nile Virus (strain WNV 956 D117 3B) encoding a subgenomic GFP replicon was provided by T. some time after acute Dengue infection. This WN/YF17D test will be particularly useful for large epidemiological studies and for screening for neutralizing antibodies against yellow fever virus. Introduction Yellow fever virus is an extremely dangerous pathogen transmitted by and mosquitoes. Recent literature reviews highlight a risk Nafamostat of transmission of this virus to currently preserved areas and Nafamostat the need to confront future large epidemics, a scenario that could be complicated by a lack of vaccine [1,2]. Since its development in the 1930s, the live attenuated vaccine against yellow fever (AAV) has been widely used, and an estimated 60 million doses are administered each year [3]. This vaccine confers protection in almost 100% of cases, and neutralizing antibodies can be detected in more than 90% of patients 10 days after vaccination and in more than 99% of patients after one month [2]. Nafamostat Until now, the protection given by the yellow fever vaccine has been estimated to last about ten years, but several studies suggest that this immunity could last for up to 30C35 years or even lifetime. The World Health Organization (WHO) has issued a report on yellow fever vaccination, concluding that the immunity given by this vaccine is stable over time and that a single dose of yellow fever vaccine is probably sufficient, with few exceptions, to provide lifetime immunity [4,5]. Consequently, at least in adults, there would be no need to re-administer a booster dose after 10 years, thus avoiding the risk of rare but serious post-vaccination complications and also sparing vaccine doses [6,7]. Indeed, worldwide production of yellow fever vaccine is relatively limited, with only 5 manufacturers producing 100 million doses per year. Despite the creation of an emergency stockpile Nafamostat by WHO, the lack of vaccine is a major risk to global public health. A reduction in the injected volume has been proposed to increase the number of vaccinations during mass campaigns, thus limiting the risk of side effects and reducing public health expenditure. Such a reduction in the injected dose, as well as combined administration with other vaccines or using other routes of injection, such as the intradermal route, must be closely evaluated in terms of immunogenicity, along with new vaccines such as the inactivated yellow fever vaccine [8C10]. The main visceral complication of vaccination is Vaccine-Associated Viscerotropic Adverse Events, particularly at the time of primary vaccination, with a high mortality rate. Post-vaccine neurological disorders may also occur after booster doses, suggesting an autoimmune phenomenon. The pathophysiology of these accidents is not fully understood and the most clearly identified risk factors are age over 60 years, a history of thymic disorders or thymectomy, as well as autoimmune diseases or genetic defects of innate immunity [6]. Finally, the increasing number of immunosuppressed travellers (patients living with HIV, cancer IRF7 or immunosuppressive treatments) requires specific monitoring of the risk-benefit ratio of yellow fever vaccination. Evaluation of vaccine protection in immunocompromised populations, as well as new dose reduction strategies, can only be evaluated in terms of immunogenicity by using surrogate biological markers, neutralizing antibodies being considered the gold standard [11]. The detection of neutralizing antibody activity is based on the reduction in the number of plaques formed by the amaril virus in cell culture by antibody neutralization (PRNT). This laboratory test, developed some 50 years ago, can only be done in specialized laboratories [12]. The PRNT has several other limitations which were recently reviewed by Jean Jonkert [13]. The PRNT measures the ability Nafamostat of a serum sample to neutralize yellow fever virus in cell culture, with a constant amount of serum and a variable amount of virus or, more often at present, a variable amount of serum and a constant dose of virus. The most widely used PRNT is based on a standardized amount of YFV17D yellow fever virus capable of forming 50 to 100 plaques in cell culture, to which serum is added at several dilutions. The correspondence between protection against yellow fever virus and the PRNT dilution titre was established in monkeys infected with yellow fever virus [14]. Survival.