GOVERNMENTS should consider stockpiling vaccine against H5N1 bird flu now, before a pandemic starts, a World Health Organization report out next month will advise. The change in policy reflects growing fears that an H5 pandemic is likely, and that there will not be time to produce much vaccine once it starts. "When we realised H5N1 is not going to be eradicated in poultry in Asia for at least another couple of years, that made the risk of H5 much higher," Klaus Stöhr, head of the WHO's influenza team, told New Scientist.
The US has already contracted manufacturers to make 4 million doses, while at a meeting at WHO headquarters in Geneva last week Italy and France said they plan to stockpile 2 million doses each. But in a world of over 6 billion people that is nowhere near enough to make a significant difference, as Stöhr points out. "This is an option only for affluent countries, and then for a fraction of their population," he says. "It won't change a lot at the global level."
Until now the WHO has said that a vaccine cannot be made until a pandemic starts, as only then can it be based on the exact strain of the virus responsible. "Normally there is no point stockpiling vaccine, because you don't know which flu will cause the next pandemic," Stöhr says. "It could be H7 or H9." But the failure to halt the H5N1 bird flu outbreaks in Asia, and the growing number of human cases (see Table), is changing minds. Recent findings also suggest that a stockpiled vaccine could provide some protection even if it does not exactly match the pandemic virus.
Experiments on animals at St Jude's Children's Hospital in Memphis, Tennessee, show that while previous exposure to similar strains may not stop them falling ill when infected with H5N1 flu, it can prevent them dying. What's more, people normally require two shots of a vaccine to make them immune to a strain of flu they have not encountered before. An H5 vaccine would prime people's immune systems, so they would need only one shot of a specific pandemic vaccine.
"My gut feeling is that if you're primed with H5, you'll respond better to the flu or to the real vaccine," says Tony Colegate of Chiron Vaccines in Liverpool, UK, who heads an international industry task force on pandemic flu. Such evidence has persuaded the experts that an H5 vaccine might help. Now the problem is making it.
So far, only half the planned US stockpile has been made, by Sanofi-Pasteur in the US. Chiron is to make the rest at a pilot factory in Liverpool that is licensed to handle the genetically engineered viruses required. But it cannot start until the problems with contamination that shut down the company's normal flu vaccine plant at the same site are cleared up. Without a dedicated factory, companies have only a two to three-month window between production runs of ordinary flu vaccine to make H5 vaccine. And they cannot even do that, Colegate says, unless someone will buy it. Then there is testing.
It is obviously impossible to find out in advance whether a vaccine will provide any protection against a pandemic strain. But it is possible to do safety tests and work out the dose needed to produce an immune response. Clinical trials of limited batches of H5 vaccine, based on the strain now circulating in Asia, are about to start in the US and are planned in Canada, Australia and Japan, all with government funding. Because these vaccines have been made at different plants using different production methods they must be tested separately.
No European governments have pledged funding for clinical trials even though most of the world's flu vaccine is made in Europe. Not everybody is convinced that spending money on testing and stockpiling an H5 vaccine is worthwhile. Albert Osterhaus of Erasmus University in Rotterdam, the Netherlands, thinks money would be better spent on stockpiling antiviral drugs, as the WHO has long recommended.
But the capacity for manufacturing antivirals is limited, and there is also no guarantee that existing drugs will work against a pandemic strain. Other leading experts think the threat is so serious that we should be doing everything we can to prepare.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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