Drugs plug gap as world awaits bird flu vaccine
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Scientists believe they have the know-how to make an effective vaccine against pandemic bird flu; the problem is how to make enough of it.
As avian flu spreads from Asia into Siberia and Kazakhstan, health experts are increasingly focused on the medical challenge of fighting the disease should it “go human” and start to spread easily from person to person.
A vaccine is the best hope to prevent millions of deaths.
But current global manufacturing capacity, at around 300 million regular flu doses a year, is simply insufficient to meet global needs during a pandemic.
“If you need to vaccinate the whole world, you are not going to do that with existing capacity, which is basically aimed at the over-65s in the West,” said Tony Colegate of Chiron Corp, who coordinates production issues for the Influenza Vaccine Supply Task Force, an international industry group.
Adding new production will take time, raising fears that many poor parts of the world are likely to go without.
At present, 90 percent of capacity is concentrated in Europe and North America, and the World Health Organization (WHO) says past experience suggests governments will be reluctant to release supplies for export before domestic demand is fully met.
There will also be a hiatus of four to six months while factories switch to making a pandemic version, once a new strain of humanized bird flu is identified.
BUYING TIME
In the absence of a vaccine, the job of holding pandemic flu at bay will rest largely on a limited stockpile of antiviral drugs, called neuraminidase inhibitors, that can reduce the severity of flu infection and can speed patients’ recovery.
This could buy valuable time to produce a vaccine and introduce other emergency measures, according to the WHO, which accepted a donation of 3 million doses of Swiss drug firm Roche’s Tamiflu medicine in August.
Britain’s GlaxoSmithKline says it may make a similar, but smaller, donation of its drug Relenza.
The hope is that intensive use of neuraminidase inhibitors in an area where a pandemic is emerging will delay its spread, or even nip it in the bud altogether.
In the meantime, scientists will be working overtime on vaccine development.
The good news is that some of the technical issues surrounding bird flu vaccine are being resolved.
Although a specific vaccine against pandemic virus cannot be made until the final strain emerges, most experts think the H5N1 strain now circulating is the one they need to target.
As with seasonal flu, the vaccine can be adjusted as the virus changes but the hope is that it will not mutate so much as to escape protection offered by the vaccines now in development.
The most advanced H5N1 vaccine, from France’s Sanofi-Aventis SA, has already proved effective at stimulating an immune system response in healthy adults and others are in the pipeline.
U.S.-based Chiron aims to test its H5N1 vaccine in the fall and GlaxoSmithKline plans large-scale clinical trials in 2006.
Even so, Nomura pharmaceuticals analyst Michael Leacock estimates only 75 million doses can be made within a year—equal to just one-quarter of current seasonal flu vaccine output.
And that would require abandoning production of vaccine for seasonal flu, which regularly kills 250,000 to 500,000 people a year.
The H5N1 strain has so far killed more than 60 people in Asia since 2003, but experts fear it will mutate into a mass killer of millions if it becomes more infectious.
CHICKEN AND EGG
Much of the problem lies in the tricky nature of flu vaccine production, which involves cultivation in embryonated chicken eggs and yields only limited amounts of antigen—the key component of a vaccine that triggers an immune response.
Stretching antigen supplies is therefore crucial.
The problem is particularly acute because the quantity of antigen needed to get a response to a bird flu vaccine is much greater than normal.
One way round this may be to use adjuvants—compounds added to a vaccine to boost the immune response—or else to inject vaccine under the skin rather than into muscle.
The long-term answer is to adopt better technology and move away from chicken egg production, which could in any case be at risk if bird flu leads to mass slaughter of poultry.
Cultivating antigen in stainless steel vats of cell culture is widely seen as the way of the future.
But David Fedson, a leading expert on flu vaccines and a former senior executive at Sanofi-Aventis, says cell culture will have little effect on capacity within the next five years.
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