?It looks like the H5N1 viruses can?t easily successfully switch genes with human flu viruses: that?s reassuring!?
Researchers from the Center for Disease Control and Prevention (CDC) in Atlanta, USA, have combined bird and human flu viruses in order to create a pandemic strain. They reported recently that the hybrid viruses are, at least for ferrets, relatively benign . Richard Webby, virologist at the St. Jude Children's Research Hospital, comments on these results for Scitizen.
Why is it interesting to combine genes from human flu virus and the H5N1 bird flu strain? What scenario is being tested?
One of the reasons why we don’t have a lot of human pandemics with these avian strains is that they don’t generally grow very well in humans or transmit between them. One way that we know that these avian viruses can adapt to humans is by getting together with a human virus and mixing gene segments. If we look back at the last 2 human pandemics, the 1967 Asian Flu and the 1968 Hong Kong Flu, those viruses came about by the avian flu virus getting together with the human flu virus and mixing genes (what we call reassortant viruses). So what the CDC researchers wanted to test was whether this could potentially be one of the mechanism by which H5N1 becomes a human pandemic virus. They did this by experimentally mixing the H5N1 virus genes with genes from a human virus and then testing the resulting reassortant viruses to see whether they could grow and transmit in ferrets. The ferret is a model very frequently used as a surrogate for human.
The recombined viruses were both less deadly than the original H5N1 strain and unlikely to transfer to other animals. What conclusion should be drawn from these results?
The conclusion from this experiment was that it looks like the H5N1 viruses can’t easily successfully switch genes with human flu viruses. That’s reassuring.
We need to keep in mind that there are a lot of different variants of flu viruses, within the H5 or within the human viruses. The limitation with doing the experiment is that you’re testing one particular bird flu virus with one particular human flu virus. Even though the avian-human virus pair they looked at appeared not to work well together, who knows, there may be others that could possibly do it.
In late August, the Global Initiative for Sharing Avian Influenza Data was launched. Do you feel that there is a lack of data sharing?
Yes, there is a lack of data and virus sharing. There are a number of reasons, it’s a very complicated issue.
Will you join the initiative?
Yes, certainly. Although we’re not very involved in the ongoing H5N1 sequencing initiatives, where we are, we will certainly follow the Global Initiative guidelines.
Would you say that pandemic vaccine show promises?
The results of the GSK’ clinical trial study certainly appear promising: they’ve put an adjuvant with very low amounts of H5 antigen and claim good results . We are eagerly awaiting the presentation of these data from this study. In the earlier trials, and particularly in the first trials in the US, you needed to put a lot of H5 antigen in the vaccine to get a response.
What we’ve seen so far is pretty much what we expected.
Richard Webby, thank you.
 T.R. Maine et al, Proc Natl Acad. Sci. USA doi:10/1073/pnas.0605134103;2006
 See GSK's press release
Richard Webby is virologist at the Department of Infectious Diseases of the St. Jude Children's Research Hospital.
Interview by Gilles Prigent