The Interplay Between Epigenetics, Vector Competence and Vaccine Immunodynamics as a Possible Explanation for Recent Yellow Fever Resurgence in Nigeria

Abstract

Background: Yellow fever virus (YFV), a member of the genus Flaviviridae is the causative agent of YFD. The virus is classified as single-stranded RNA which is mostly transmitted by mosquitoes identified by Walter Reed in the year 1900 as Aedes aegypti [4]. In the past, Nigeria had been facing asporadic outbreaks of Yellow fever (YF), which began with the populous Northern region of the country. Aedes species of mosquitoes mainly transmit yellow fever virus (YFV) and vaccination is the only effective means of preventing it.
Objectives: This article presents a critical review and literature updates on the vector biology, YF vaccine immunodynamics and epigenetics of YFV, with the aim to understand the interplay of these factors in the re-emergence of YF and risk assessment of living or traveling to YF endemic areas. (in the year 2016-2018)
Methodology: The live, attenuated viral strain of the 17D vaccine was administered to tourists and inhabitants of endemic regions of Africa (Figure: 2) and South America. Those eligible for the vaccine were usually given through routes of administration either by single subcutaneous or intramuscular injection. The vaccine (17D-204 strain) could be given either to infants (pediatric dosage) above 9 months or adults (adult dosage) using one dose of subcutaneous injection (≥4.74 log10 plaque-forming units/0.5mL) not later than 10 days to regional migration
Conclusion: Vectorial migration, jungle-to-urban spillover, immunization failure (especially in persons with chronic immune-mediated inflammatory diseases) and perhaps, genetic modification of YFV could be reasons for the resurgence of YF in the country. The single dose of the vaccine was usually sufficient to confer prolonged immunity against the infection but booster doses were often required based on endemic state of certain countries' Medical Laboratory Staff who frequently work on wild-type yellow fever virus. Based on regular exposure to this virus on routine basis, the neutralizing antibody titers against the virus are usually assessed every ten years to determine the necessity for booster doses of the 17D vaccine. Irrespective of the knowledge of neutralizing antibody titers for the virus, vaccination every 10 years is recommended especially for individuals frequently exposed to the vir
Recommendations: Increase vaccination coverage. Include YF vaccine in childhood vaccination programs. Make effort to maintain and control future outbreaks.

Keywords: Vaccination, Genetics, Yellow Fever, Re-emergence