Promising preclinical results with live attenuated H5N...( Several approaches are in progress to ...)

Several approaches are in progress to develop vaccines against the avian flu variety of the influenza virus. Kanta Subbarao (National Institutes of Health) and colleagues are working on live attenuated vaccines, which have the potential to elicit a strong, broad, and lasting immune response. As they now report in the international open-access medical journal PLoS Medicine, results from mice and ferrets (the rodent flu model of choice) are very encouraging and pave the way to testing these vaccines in human volunteers.

The researchers developed vaccines using 3 artificially constructed, weakened forms of the influenza virus. The 3 vaccine viruses were constructed using flu virus proteins other than H and N from artificially weakened (attenuated) strains of influenza. These were combined with H and N proteins from H5N1 viruses isolated from human cases during three different years: 2004, 2003, and 1997. They grew larger quantities of the resulting viruses in hen eggs, and tested the vaccines in chickens, ferrets, and mice.

In tests of safety, the study found that, unlike the natural viruses from which they were derived, the vaccine strains did not cause death when injected into the bloodstream of chickens, and did not even cause persistent infection when given through the birds' breathing passages. Similarly, while the natural viruses were lethal in mice at various doses, the vaccine strains did not cause death even at the highest dose. In ferrets, infection with the vaccine strains was limited to the upper respiratory tract, while the natural viruses spread eadily to the lungs.

In tests of protection, all mice that had received any of the 3 vaccines survived following injection with any of the natural viruses (so-called viral challenge), while unvaccinated mice died following viral challenge. This occurred even though standard blood tests could not detect a strong immune responses following a single dose of vaccine. Challenge virus was
'"/>

Contact: Andrew Hyde
press@plos.org
44-122-346-3330
Public Library of Science
11-Sep-2006