[Show abstract][Hide abstract] ABSTRACT: Wild type human influenza viruses do not usually grow well in embryonated hens' eggs, the substrate of choice for the production of inactivated influenza vaccine, and vaccine viruses need to be developed specifically for this purpose. In the event of a pandemic of influenza, vaccine viruses need to be created with utmost speed. At the onset of the current A(H1N1) pandemic in April 2009, a network of laboratories began a race against time to develop suitable candidate vaccine viruses. Two approaches were followed, the classical reassortment approach and the more recent reverse genetics approach. This report describes the development and the characteristics of current pandemic H1N1 candidate vaccine viruses.
[Show abstract][Hide abstract] ABSTRACT: Diversidad antigénica y genética de aislamientos del virus de Influenza Aviar de alta patogenicidad subtipo H5N1 en Egipto. El subtipo H5N1 de Influenza Aviar de alta patogenicidad ha mostrado diversidad antigénica y genética desde su detección inicial en Asia en el año 1997. En particular, los virus pertenecientes al clado 2.2 han sido reportados en numerosos países, en su mayoría provenientes de casos observados en Egipto. Reportes previos identificaron similitudes antigénicas entre los virus pertenecientes al clado 2.2. Sin embargo, los virus aviares y humanos aislados en el norte de Egipto durante los años 2007 y 2008 fueron antigénicamente distintos de otros virus del clado 2.2 de este país. El análisis genético de la hemaglutinina reveló un alto grado de divergencia de los nucleótidos y aminoácidos. Los cambios antigénicos observados en los virus egipcios aislados durante el 2007 y el 2008 hacen necesario que dos de estas cepas se consideren como candidatas potenciales a ser virus vacunales H5N1 pre-pandémicos. Abbreviations: CDC = Centers for Disease Control and Prevention; CLEVB = Central Laboratory for Veterinary Biologics Evaluation; GS/GD = A/Goose/Guangdong/1/96; HA = hemagglutinin; HI = hemagglutination inhibition; HPAI = highly pathogenic avian influenza; NAMRU-3 = U.S. Naval Medical Research Unit No. 3; NLQP = National Laboratory for Quality Control of Poultry Production; PBS = phosphate buffered saline; RT-PCR = reverse transcription-polymerase chain reaction; WHO = World Health Organization
[Show abstract][Hide abstract] ABSTRACT: Highly pathogenic avian influenza A virus (H5N1) has diverged antigenically and genetically since its initial detection in Asia in 1997. Viruses belonging to clade 2.2 in particular have been reported in numerous countries with the majority occurring in Egypt. Previous reports identified antigenic similarities between viruses belonging to clade 2.2. However, poultry and human viruses isolated in northern Egypt during 2007 and 2008 were found to be antigenically distinct from other clade 2.2 viruses from this country. Genetic analysis of the hemagglutinin revealed a high degree of nucleotide and amino acid divergence. The antigenic changes in Egyptian viruses isolated during 2007-08 necessitated that two of these strains be considered as potential H5N1 pre-pandemic vaccine candidates.
[Show abstract][Hide abstract] ABSTRACT: High pathogenicity avian influenza H5N1 has become an endemic poultry disease in several Asian countries, including Vietnam. Recently, dade 7 H5N1 viruses of the Eurasian lineage were isolated from chickens seized at ports of entry in Lang Son Province, Vietnam. Extensive nucleotide and amino acid divergence across the hemagglutinin (HA) protein gene of these isolates in comparison to previously described clade 7 viruses was identified. Clade 7 viruses are antigenically distinct from contemporary strains of H5N1 known to circulate in Vietnamese poultry (clade 1 and clade 2.3.4). Subsequent surveillance of sick poultry in live poultry markets in Hai Duong Province identified additional clade 7 isolates with HA genes very similar to the group B virus cluster detected previously at the Lang Son Province border. Antigenic analysis of the isolates from the live bird markets revealed significant cross-reactivity only between those clade 7 viruses belonging to the same subgroups. To meet pandemic response preparedness objectives, we have developed a reassortant virus from A/chicken/Vietnam/NCVD-016/2008, which could be used as a new prepandemic vaccine candidate for veterinary or human vaccination, should the need arise. Findings from these studies indicate that viruses with clade 7 HA have continued to evolve in Southeast Asian poultry, leading to significant antigenic drift relative to other H5N1 viruses currently circulating in Vietnam.
[Show abstract][Hide abstract] ABSTRACT: Highly pathogenic H5N1 avian influenza viruses currently circulating in birds have caused hundreds of human infections, and pose a significant pandemic threat. Vaccines are a major component of the public health preparedness for this likely event. The rapid evolution of H5N1 viruses has resulted in the emergence of multiple clades with distinct antigenic characteristics that require clade-specific vaccines. A variant H5N1 virus termed clade 2.3.4 emerged in 2005 and has caused multiple fatal infections. Vaccine candidates that match the antigenic properties of variant viruses are necessary because inactivated influenza vaccines elicit strain-specific protection.
To address the need for a suitable seed for manufacturing a clade 2.3.4 vaccine, we developed a new H5N1 pre-pandemic candidate vaccine by reverse genetics and evaluated its safety and replication in vitro and in vivo.
A reassortant virus termed, Anhui/PR8, was produced by reverse genetics in compliance with WHO pandemic vaccine development guidelines and contains six genes from A/Puerto Rico/8/34 as well as the neuraminidase and hemagglutinin (HA) genomic segments from the A/Anhui/01/2005 virus. The multi-basic cleavage site of HA was removed to reduce virulence.
The reassortant Anhui/PR8 grows well in eggs and is avirulent to chicken and ferrets but retains the antigenicity of the parental A/Anhui/01/2005 virus.
These results indicate that the Anhui/PR8 reassortant lost a major virulent determinant and it is suitable for its use in vaccine manufacturing and as a reference vaccine virus against the H5N1 clade 2.3.4 viruses circulating in eastern China, Vietnam, Thailand, and Laos.
Influenza and Other Respiratory Viruses 11/2009; 3(6):287-95. · 1.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Vaccination will be a critical public health intervention to mitigate the next influenza pandemic. Its effectiveness will depend on preparedness at multiple levels, from the laboratory bench to the population. Here we describe a global approach to ensure that appropriate candidate vaccine viruses are produced, evaluated, and made available to vaccine manufacturers in a timely fashion. This is an integrated activity involving global virologic and epidemiologic surveillance, genetic and antigenic characterization of influenza viruses, pandemic risk assessments, selection of appropriate virus strains for vaccines, production of reassortant viruses by reverse genetics, and finally, analysis of their safety and growth characteristics prior to distribution. These procedures must comply with national and international regulations governing vaccine and environmental safety.
Current topics in microbiology and immunology 01/2009; 333:83-108. · 4.86 Impact Factor