Researchers from the National Institutes of Health and University of Maryland report that a new vaccine that protects monkeys against the avian influenza virus is now a candidate for clinical trial in humans. The rate of transmission of the highly pathogenic avian influenza virus (HPAIV) from birds to humans is rapidly increasing.
The H5N1 strain is responsible for 278 known human infections resulting in 168 deaths. The possibility of a pandemic outbreak emphasizes the need for an effective vaccine, however development has been impeded by factors such as poor immunogenicity, biosafety concerns, and risk of genetic exchange with circulating influenza virus strains.
In the study researchers developed a live vaccine incorporating the avian Newcastle disease virus (NDV), which expresses a common gene found in the H5N1 avian influenza virus, and tested it in African monkeys. The vaccine was administered both intranasally and through the respiratory tract in two doses with a 28-day interval in between.
Response after one dose showed low amounts of virus shedding indicating protection. Following two doses, high levels of neutralizing antibodies were present in all immunized monkeys. A substantial response to either dosage was noted in the respiratory tract indicating a likely reduction in transmission in the event of an outbreak.
"In this study, we have developed a vaccine candidate, NDV-HA, for immunization against H5N1 HPAIV and have tested it in a nonhuman primate model," say the researchers. "The vaccine was well tolerated and induced substantial local and systemic immune responses, demonstrating that NDV has potential as a live virus candidate vaccine against HPAIV."
Journal reference: J.M. DiNapoli, L. Yang, A. Suguitan Jr., S. Elankumaran, D.W. Dorward, B.R. Murphy, S.K. Samal, P.L. Collins, A. Bukreyev. 2007. Immunization of primates with a Newcastle disease virus-vectored vaccine via the respiratory tract induces a high titer of serum neutralizing antibodies against highly pathogenic avian influenza virus. Journal of Virology, 81. 21: 11560-11568.
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