ABSTRACT
Yellow fever(YF) is a natural focal disease transmitted by infected mosquitoes,which had caused epidemic in some areas of Europe and America port city in the history,bringing great disaster to human society.Since 40s of last century,a series of derivative strain of 17D vaccines,providing lifelong protection,had been vaccinated a large population who are trave ling to or living in areas at risk for YF,which avoid the outbreak of the disease,appearing quiet state.Since the beginning of 1990s,the disease had outbreak successively in Africa,tropical American areas and its nations.The mortality was even more higher than Ebola happened in 3 countries in West Africa between 2014 and 2015.In 2016-2017the large outbreak in Angola,Congo and Brazil,has claimed thousands of lives.Yellow fever has never occurred in Asia until the introduction of 11 cases by jet travel from Angola to China,which attracted the attention of Chinese government.Yellow fever elimination initiative strategic plan for 2017 2026 was launched by WHO,mainly based on that 17D vaccine which is safe and effective to control the spread of this disease.The measures of controlling mosquitoes and vaccination programs,in particular putting great expectations for the latter,are the main measures for prevention the disease and achievement the goal of WHO elimination strategic plan.But strong guarantees of related countries and abiding by the provisions of the global quarantine regulations are also important.Therefore,this article reviews the historical and the recent epidemic outbreaks of yellow fever,vaccination and other prevention measures,hoping that the WHO elimination of the yellow fever epidemic strategy will achieve successfully in 2026.
ABSTRACT
La vacuna colombiana 17D contiene por lo menos cuatro fenotipos, denominados pequeño (0,3-1,2 mm), mediano (1,3 -2,1 mm), grande (2,2 - 3,0 mm) y extra-grande (>3,1 mm). La composición y distribución porcentual de esos fenotipos variaron entre lotes y entre ampolletas de un mismo lote. Cada variante fue clonada por dilución de la vacuna y su efecto virulento fue analizado en ratones; el fenotipo de placa pequeño estuvo ligeramente sub representado en los lotes analizados y mostró una virulencia similar a la de la cepa silvestre neurotrópica francesa (DL50 >10-6), mientras que el fenotipo predominante y más atenuado fue el mediano (DL50:10-4). Los fenotipos grande y extragrande mostraron una virulencia intermedia (DL 50:10-5) con relación a los anteriores. Los análisis de secuencia de las variantes sobre una región comprendida entre el extremo 3'NS5 y el inicio de 3'NCR mostró la cercanía entre aquellas variantes con algún grado de virulencia, y entre la variante atenuada y la vacuna colombiana. La heterogeneidad de la vacuna 17D constituye una evidencia de la estructura de cuasiespecies propia de los virus RNA, y señala cómo los casos de reacciones pos vacunales adversas pueden estar asociados con la aplicación de vacunas fabricadas a partir de cepas virales atenuadas.
The Colombian 17D vaccine contains at least four phenotypes denominated small (0.3 - 1.2 mm), medium (1.3 - 2.1 mm) large (2.2 - 3.0 mm) and extra-large (>3.1 mm). These phenotypes composition and percentage distribution vary between different production lots and between ampoules from a particular lot. Each variant was cloned by diluting the vaccine and its virulent effect was analysed in young mice. The small plaque phenotype was slightly under represented in the lots analysed and showed similar virulence to the neurotropic French wild strain (LD50 >10-6), whilst the medium- sized phe-notype predominated and was the most attenuated (LD50:10-4). The large and extra-large phenotypes showed intermediate virulence (LD50:10-5) regarding the others. Sequence analysis of variants within the region between the 3'NS5 end and the beginning of 3'NCR showed the closeness between those variants having some degree of virulence and between the attenuated variant and the Colombian vaccine. The 17D vaccine's heterogeneity constitutes evidence of RNA virus quasi-specie structure and shows how adverse yellow fever vaccine reaction can be associated with applying vaccines produced from attenuated viral strains.
A vacina colombiana 17D, contém pelo menos quatro fenótipos, denominados pequeno (0.3 - 1.2 mm), médio (1.3 -2.1mm), grande (2.2 - 3.0mm) e extra grande (>3.1 mm). A composição e distribuição percentual destes fenótipos, variou entre lotes e ampolas do mesmo lote. Cada variante foi clonada por diluição da vacina e seu efeito viral foi analisado em ratos; o fenótipo da placa pequena, esteve ligeiramente sub-representado nos lotes analisados e mostrou uma virulência similar a da cepa silvestre neurotrópica francesa (LD50 >10-6), enquanto que, o fenótipo predominante e mais atenuado foi o médio (LD50:10-4). Os fenótipos grande e extra grande mostraram um estado viral intermediário (LD50:10-5) com relação aos anteriores. As análises da seqüência das variantes sobre uma região compreendida entre o extremo 3'NS5 e o início de 3'NCR, mostrou a proximidade entre aquelas variantes com algum grau de virulência, e entre a variante atenuada e a vacina colombiana. A heterogeneida-de da vacina 17D, constitui uma evidência da estrutura de qualquer espécie própria do vírus RNA e assinala como os casos de reações pós vacinação adversas, podem estar associadas com a aplicação das vacinas fabricadas a partir das cepas virais atenuadas.