Bird flu: of mice and men
A STUDY shows that live attenuated vaccine based on a single H5N1 virus strain can provide protection (in mice and ferrets, at least) against different H5N1 viruses that emerge years later.
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.
The researchers developed vaccines using three artificially constructed, weakened forms of the influenza virus.
Flu virus proteins
The three 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. While the natural viruses were lethal in mice at various doses, the vaccine strains did not cause death even at the highest dose.
Encouraging results
As they now report in the international open-access medical journal PLoS Medicine, results from mice and ferrets are very encouraging.
In tests of protection, all mice that had received any of the three vaccines survived following injection with any of the natural viruses (so-called viral challenge), while unvaccinated mice died following viral challenge.
Mice and ferrets that had received two doses of vaccine were protected against challenge with H5N1 strains from more recent outbreaks in Asia that differed substantially from the strains that were used for the vaccine.
Mice given two doses of a vaccine showed stronger immunity on blood tests, as well as almost complete protection from respiratory infection following challenge.
One of the vaccines is now being tested in human volunteers who participate in carefully conducted clinical trials. — Our Bureau
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