Friday, March 31, 2006
http://vitualis.blogspot.com/2006/03/bird-flu-vaccines-fail.html
Bird flu vaccines fail
The H5N1 avian influenza (bird flu) virus continues its steady march across the globe. Over the course of the past year, it has followed migratory birds and spread from South-East Asia into Africa, Eastern Europe and even Western Europe (France and Germany).
Thankfully, there has been no evidence of a mutation to a human-to-human transmissible form and although the number of human victims have been ticking upwards, the feared pandemic has not arrived, yet. On the other hand, treatment options against bird flu are limited, and perhaps even more so than would be expected. Although world governments have been stockpiling neuraminidase inhibitors like oseltamivir (Tamiflu) and zanamivir (Relenza) there is increasingly dissent on the usefulness of these drugs. Resistance to these agents have already been found in mutations of the bird flu virus. Furthermore, it does not appear that these agents have improved survival in the victims of bird flu.
Perhaps most worrying of all has been the abysmal failure of the attempts to create a bird flu vaccine. In the event of a potential pandemic, an effective vaccine is in all likelihood the only defence. In February 2006, Australian company CSL Ltd announced that the trial of their vaccine had failed. Only half of those who received two shots of the highest dose had a response comparable to the regular influenza vaccine. In the past several days, French rival Sanofi-Pasteur announced that their vaccine had failed as well. Only at a dose equivalent to 12 times the usual did it provide adequate protection – and then like the Australian trial, only in half of subjects.
Although the obvious answer may seem to be that we should simply use a higher dose of the bird flu vaccine as a standard regimen, this is not feasible. These vaccines need to be grown in a rather laborious method and large individual doses would make it impossible to supply enough vaccine to protect the population.
Research is continuing feverishly though I fear that we may well lose this race against time.
From: New Scientist
Bird flu vaccine trial gives disappointing results (excerpt)
23:00 29 March 2006
NewScientist.com news service
Debora MacKenzie
...John Treanor, at the University of Rochester, New York, US, and colleagues tested a vaccine made by the French-owned firm Sanofi-Pasteur. It contained the vaccine “seed strain” of H5N1 created in 2004, grown in eggs, killed and split, the way standard flu vaccines are made.
But like earlier trials with a similar preparation, the vaccine elicited a significant immune response only when given as two doses of 90 micrograms each. This is twelve times the amount needed in standard flu vaccines. And even that worked only in about half the people tested.
Because only limited amounts of vaccine virus can be grown in the short time available at the start of a pandemic, the smaller the dose needed to immunise someone, the more people can be vaccinated in time to benefit...
...Since these results started emerging late in 2005, trial H5N1 vaccines being tested worldwide have included immune-stimulating chemicals called adjuvants, says David Fedson, founder of the vaccine companies’ pandemic task force. But two studies, one in France by Sanofi-Pasteur, and one by the Australian firm CSL announced in February 2006, found that the most common adjuvant, alum, did not help enough...
...Scientists are beginning to suspect that something about the chemical nature of the H5N1 surface proteins used in the vaccine, possibly the strategic placement of a sugar group, keeps the human immune system from responding as it usually does to flu proteins...
