Bird flu vaccine only works at highest dose: study

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) – An experimental vaccine against H5N1
bird flu only appears to work at the very highest doses,
meaning it will be harder than feared to protect the population
against a pandemic, researchers said on Wednesday.

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 in a telephone briefing before
the findings appeared in the New England Journal of Medicine.

These findings mean there is only enough H5N1 vaccine now
in the U.S. stockpile to protect about 4 million Americans in a
pandemic, Fauci said. These would likely be key health-care
workers and people working to make the vaccine.

Everyone else would have to wait while a pandemic spreads,
relying on public-health measures such 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.

It remains difficult for humans to catch but has infected
186 people in eight countries and killed 105, according to the
latest World Health Organization figures. Experts fear the
virus could evolve into a form passed easily from human to
human, causing a pandemic that could kill tens of millions.

SQUEEZING OUT EXPERIMENTS

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 globally.

Several companies and the U.S. 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, published in the New
England journal.

They said trials were underway in elderly persons, persons
with impaired immunity, or children, who may 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 only use one strain. But with two
90-microgram doses needed to produce a satisfying immune
response, current manufacturing capacity falls far short, Fauci
and Treanor said.

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

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

Fauci said the hope is that U.S. suppliers including
Sanofi, Chiron Corp., GlaxoSmithKline and MedImmune will make
120 million doses of seasonal flu vaccine this year.

GETTING UP TO SPEED

“It is going to take quite a while to get that type of
vaccine-manufacturing capacity up to scale,” Fauci said.

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

Some are also looking at faster and more modern production
methods.

Dr. Gregory Poland of the Mayo Clinic in Rochester,
Minnesota noted the antibody response measured in the study
does not always protect people from sickness with flu, but
rather lowers the risk of death and serious complications.

He said work also is underway to make a vaccine against a
second substrain of H5NI that has started to kill people.