Published Date: 2004-01-25 23:50:00
Subject: PRO/AH/EDR> Avian influenza A (H5N1) virus, human vaccine prospects
Archive Number: 20040125.0300
AVIAN INFLUENZA A (H5N1) VIRUS, HUMAN VACCINE PROSPECTS
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Sun 25 Jan 2004
From: ProMED-mail <email@example.com>
Source: Nature Science Update, Fri 23 Jan 2004 [edited]
Prospects for an Avian Influenza A (H5N1) Human Vaccine
Researchers eyeing the outbreak of avian influenza in Asia are stepping up
efforts to prepare a vaccine -- but the process could take months, they
warn. The strain of avian flu called H5N1 has killed 7 people in Vietnam,
according to the World Health Organization (WHO). Another 2 cases were
reported in Thailand on Friday. These patients -- both children -- are
still alive. The disease has devastated bird flocks in South Korea, Vietnam
and Japan [and now Thailand, Cambodia, and probably Indonesia. - Mod.CP].
"The extent of this outbreak is unprecedented," says Alan Hay, who heads
the WHO's Influenza Collaborating Centre in London.
The more people who are infected, the greater the risk that the virus might
spark a worldwide pandemic by gaining the ability to jump easily from
person to person. This could happen if the strain mutates or exchanges
genes with a human flu virus. Hay says that WHO officials are working
frantically to gauge the full scale of the avian epidemic and find out
whether there are more, as yet undiscovered, human cases or signs of
"We really do not know the extent of the problem," he says. The WHO is
already sending out reagents that can identify H5N1 to European labs in
case the virus starts to spread, says virologist Ron Fouchier at Erasmus
University in Rotterdam, the Netherlands. "Everyone's preparing for the
worst-case scenario," he says. In the face of this threat, researchers are
ramping up efforts to develop a human vaccine that might block the advance
of a potential pandemic. The vaccine is made by engineering a suitable
vaccine strain of influenza so that it does not cause disease and then
growing it in large quantities of hen's eggs.
2 laboratories, at St Jude Children's Research Hospital in Memphis,
Tennessee, and the National Institute for Biological Standards and Control
in Potters Bar, UK, already have prototype influenza strains that might be
used to mass-produce a [vaccine]. These were developed using the H5N1 avian
influenza virus that killed one man in Hong Kong in 2003. Experts are
testing whether animals inoculated with these strains produce antibodies
that also fight the 2004 virus. In a 2nd approach, WHO collaborators are
preparing a new vaccine strain from the 2004 virus using a technique called
reverse genetics. They aim to genetically engineer a milder form of the virus.
To figure out exactly how to construct the vaccine strain, scientists are
keenly awaiting word on the genetic sequence of the H5N1 virus taken from
patients and birds in Asia. Initial results from Vietnamese samples show
that the H5N1 virus has mutated since 2003, says a WHO statement.
Even armed with the prototype strain, there are several obstacles to
mass-producing the vaccine. Simply finding enough hen eggs to grow the
vaccine will be difficult, as most are already set aside for making normal
flu shots. "It'll be a matter of dragging together enough eggs," says flu
researcher Richard Webby of St Jude Children's Research Hospital. Drug
regulatory authorities might also balk at approving a human influenza
vaccine made using reverse genetics -- such vaccines haven't yet progressed
through clinical trials. Even if these roadblocks can be overcome, experts
estimate that mass-production of the vaccine will take at least 3 months.
In the absence of a vaccine, antiviral drugs such as Tamiflu should form a
first line of defence against a pandemic flu strain, says Fouchier.
Tamiflu was used to curb the spread of an avian influenza outbreak in the
Netherlands in 2003, which killed one man.
[Byline: Helen Pearson]
[See ProMED-mail post "Avian influenza A (H5N1) virus, drug resistance" for
discussion of containment of avian influenza by drug treatment. - Mod.CP]