Bird flu vaccine falls well short of hopes

An experimental vaccine against bird flu appears to work only at the very highest dosage level.

The disappointing result highlights the urgency of brewing a better vaccine.

The United States Government had hinted that the vaccine had serious flaws last year, even as it ordered US$162 million ($266 million) of shots to stockpile in case the bird flu mutated to spread easily from person to person.

The vaccine, made by a unit of Sanofi-Aventis and based on an H5N1 virus that killed a Vietnamese man in 2004, only produced a satisfactory immune response in volunteers at two doses of 90 micrograms each.

That is 12 times what is needed for the annual seasonal flu shot.

"It is a bit of muted good news in that we are going in the right direction, but the sobering news is we have a long way to go," National Institute of Allergy and Infectious Diseases director Dr Anthony Fauci said before the findings appeared in the New England Journal of Medicine.

These findings mean there is only enough H5N1 vaccine now in the US stockpile to protect about 4 million Americans in a pandemic.

Dr Fauci said these would probably be key healthcare workers and people working to make the vaccine.

Everyone else would have to wait while a pandemic spread, relying on public-health measures such as social distancing - meaning closing businesses, schools and using masks, gloves and other protective equipment - in the meantime.

The H5N1 avian influenza virus has spread in birds at an alarming rate in recent months, sweeping out of east Asia across to Europe and down into Africa. Officials believe it will become entrenched in wild birds across the globe within a year or two.

Experts fear that the virus could evolve into a form passed easily from human to human, causing a pandemic that could kill tens of millions.

Because influenza viruses mutate quickly, it is impossible to prepare a vaccine in advance that would precisely match a pandemic strain. And flu vaccine capacity is extremely limited because of low demand, even though seasonal influenza kills more than 250,000 people every year.

Several companies and the US National Institutes of Health are working on H5N1 vaccines, squeezing in production at corporate factories during lulls in making the annual seasonal flu vaccine.

Dr John Treanor, of the University of Rochester in New York, and colleagues tested Sanofi-Pasteur's experimental H5N1 vaccine on 450 volunteers.

"Only the 90-microgram dose was associated with antibody responses," they wrote in their report.

They said trials were under way in elderly persons, persons with impaired immunity, or children, who might have a different response.

The annual flu vaccine mixes the three most common circulating strains of flu at 15 micrograms each. A pandemic vaccine would probably use only one strain.

But with two 90-microgram doses needed to produce a satisfactory immune response, Drs Fauci and Treanor said manufacturing capacity fell far short.

Most people need only a single dose of seasonal flu vaccine.

Global capacity for making influenza vaccines is 900 million doses. The US would need vaccine to protect 300 million people, but the most companies have made for the American market is 83 million doses.

More than 30 trials of an H5N1 vaccine are under way, many of which look at ways to stretch the vaccine by lowering the dose and adding other drugs to boost the immune response.


Limited protection

* Human testing with an experimental bird flu vaccine sparked a protective immune response in disappointingly few people - 54 per cent of those who got two shots, 28 days apart, of the highest dose.

* Regular winter flu shots, in contrast, protect 75 to 90 per cent of young healthy people, the same group that first tested the bird flu vaccine. More than 180 people worldwide, mostly in Asia, are known to have been infected with the H5N1 virus since 2003; more than 100 have died. Virtually all had close contact with sick poultry.

- REUTERS