Leading infectious disease experts yesterday called on for the separate stockpiling of additives, or adjuvants, to help boost the effectiveness of vaccines to fight the next flu pandemic.
Experts have warned for years that a flu pandemic is long overdue and scientists at a conference in Bangkok said the H5N1 bird flu virus remained a key candidate, but another avian influenza virus could also unleash such a catastrophe.
Albert Osterhaus, a microbiologist at the Erasmus Medical Center in the Netherlands, said stockpiling adjuvants might well be the solution if another virus ended up stealing the show.
"There's a lot of discussion to vaccinate people against H5N1 with adjuvanted vaccines. We might do that, but it's very expensive and it might well be that the pandemic outbreak may not be caused by H5N1 but by H7, H9 or H2" viruses, he said.
There are many types of bird flu viruses and they are divided into subtypes on the basis of two proteins on their surfaces; the "H protein" hemagglutinin and "N component" neuraminidase. The H protein allows the virus to attach to receptors on the surface of an animal cell.
There are 9 subtypes of hemagglutinin proteins and 16 neuraminidase proteins, meaning there exists in nature dozens of bird flu virus combinations, some of which could be a threat to humans.
The strains that are known to have already infected humans but yet not caused a pandemic are H5N1, H7N3, H7N7 and H9N2.
Vaccines are created with antigens, or substances such as toxins, viruses and bacteria that stimulate the production of antibodies when introduced into the body.
But because there will not be enough antigen to go around in a pandemic, experts have been trying to address that problem by using boosters, such as adjuvants.
Osterhaus said adjuvants should be stockpiled separately from antigens.
"Adjuvants can be stockpiled and H5 antigen as well. So if the pandemic is going to be H5N1, you just mix them and you get a vaccine," he said.
"If not, you rapidly produce the antigen and add it together with the adjuvant."
Other speakers at the three-day conference called for a wider approach to pandemic preparedness, but they stressed that H5N1 was likely to be the most lethal candidate.
Although the virus has infected only 351 people around the world since 2003, it has killed 219 of them, according to the World Health Organization.
Don't blame wild birds
There is no solid evidence that wild birds are to blame for the apparent spread of the H5N1 virus from Asia to parts of Europe, Africa and the Middle East, an animal disease expert said yesterday.
There was also no proof that wild birds were a reservoir for the H5N1 virus, Scott Newman, international wildlife coordinator for avian influenza at the UN's Food and Agriculture Organization, said.
But Newman said there was no good reason for thinking so.
"We know that some wild birds have probably moved short distances carrying viruses and then they died, but we have not been able to identify carriage of H5N1 across large scale spatial distances and then resulting in spread to other birds and mortality in poultry flocks," Newman said.
He said fecal tests on some 350,000 healthy birds worldwide had to date only yielded "a few" positive H5N1 results.
Source: China Daily/Agencies
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