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
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A ProMED-mail post
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International Society for Infectious Diseases
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Date: Sun 25 Jan 2004
From: ProMED-mail <promed@promedmail.org>
Source: Nature Science Update, Fri 23 Jan 2004 [edited]
<http://www.nature.com/nsu/040119/040119-15.html>
Prospects for an Avian Influenza A (H5N1) Human Vaccine
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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
human-to-human transmission.
"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]
--
ProMED-mail
<promed@promedmail.org>
[See ProMED-mail post "Avian influenza A (H5N1) virus, drug resistance" for
discussion of containment of avian influenza by drug treatment. - Mod.CP]
See Also
Avian influenza A (H5N1) virus, drug resistance - to be archivedAvian influenza, human - East Asia 20040124.0283
Avian influenza, Eastern Asia (03): RFI 20040118.0206
Avian influenza, falcon - China (Hong Kong) 20040121.0243
Avian influenza, human - Thailand (02): confirmed 20040123.0262
Avian influenza, human - Thailand (03) 20040123.0268
Avian influenza, human - Thailand: suspected 20040122.0247
Avian influenza, human - Vietnam (02) 20040113.0138
Avian influenza, human - Vietnam (03) 20040114.0154
Avian influenza, human - Vietnam (04) 20040114.0155
Avian influenza, human - Viet Nam (05) 20040117.0181
Avian influenza, human - Vietnam (06) 20040118.0193
Avian influenza, human - Vietnam (07) 20040119.0213
Avian influenza, human - Vietnam (08) 20040119.0216
Avian influenza, human - Vietnam (09) 20040120.0225
Avian influenza, human - Vietnam (10) 20040122.0251
Avian influenza, human - Vietnam (11) 20040122.0258
Avian influenza, human - Vietnam: RFI 20040112.0127
Avian influenza, Taiwan - OIE 20040123.0273
Avian influenza, Thailand - OIE 20040124.0276
Avian influenza, WHO fact sheet 20040116.0171
Avian influenza - Eastern Asia 20040114.0145
Avian influenza - Eastern Asia (02) 20040116.0176
Avian influenza - Eastern Asia (04): RFI 20040119.0208
Avian influenza - Eastern Asia (05) 20040120.0222
Avian influenza - Japan (02) 20040112.0125
Avian influenza - Japan (03): OIE 20040114.0151
Avian influenza - Japan: RFI 20040111.0124
Avian influenza - Taiwan: not 20040114.0148
Avian influenza - Taiwan ex mainland China: susp. 20040101.0001
Avian influenza - Thailand (02): not 20040109.0097
Avian influenza - Thailand: RFI 20040105.0051
Avian influenza - Vietnam (02) 20040110.0106
Avian influenza - Vietnam: OIE 20040109.0101
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