Published Date: 2004-01-20 23:50:00
Subject: PRO/AH/EDR> Avian influenza, human - Vietnam (09)
Archive Number: 20040120.0225
AVIAN INFLUENZA, HUMAN - VIETNAM (09)
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Date: Tue 20 Jan 2004
From: Marianne Hopp <mjhopp12@yahoo.com>
Source: World Health Organisation (WHO), CSR, Tue 20 Jan 2004 [edited]
<http://www.who.int/csr/don/2004_01_20/en/>
Development of a Vaccine Effective against Avian Influenza H5N1 Infection
in Humans - WHO Update 4
--------------------------------------------------
The WHO influenza pandemic preparedness plan, issued in 1999, sets out a
series of steps to be taken following confirmation of human infection with
a new influenza virus subtype not yet spreading from person to person. One
of these steps concerns the initiation of research needed for vaccine
production.
As a precautionary measure, WHO is moving forward with the procedures
needed to rapidly produce a new influenza vaccine capable of protecting
humans against the H5N1 strain of avian influenza recently detected in Viet
Nam. These procedures have been initiated following mounting concern over 5
laboratory-confirmed human cases of H5N1 avian influenza in Hanoi, Viet Nam
in recent weeks. All 5 cases were fatal.
The human deaths in Viet Nam coincide with historically unprecedented
epidemics, in bird populations, of highly pathogenic H5N1 avian influenza
in Viet Nam, the Republic of Korea, and Japan. The epidemic in birds is the
1st in Japan since 1925, and the 1st ever documented in Viet Nam and the
Republic of Korea.
Prototype viruses for vaccine production are being prepared by laboratories
in the WHO Global Influenza Network. Several laboratories in this network
have the high-security (biosafety level 3) facilities needed to
safely conduct work on a highly pathogenic virus such as H5N1. Prototype
viruses are then supplied to manufacturers as the "seed stock" for vaccine
production.
Laboratories in Hong Kong and Japan have isolated the virus from specimens
obtained from 2 of the laboratory-confirmed fatal cases in Viet Nam. The
virus is now being analysed at the molecular level to obtain information
about its origin and its relationship to viruses currently circulating in
birds and possibly other animals. These studies will also determine the
antigenic and genetic characteristics of the virus that are needed to
produce a candidate vaccine.
Using laboratories in the WHO influenza network, and following procedures
established by WHO to detect and respond to a new influenza virus subtype,
[researchers could make] a prototype virus available to vaccine
manufacturing companies within about 4 weeks.
Candidate vaccines were developed in 2003 by network laboratories in
London, UK and Memphis, Tennessee, USA for protection against the H5N1
virus strain, which caused 2 cases and one death in Hong Kong in February 2003.
If the virus isolated from the fatal cases in Viet Nam proves sufficiently
similar to the 2003 H5N1 strain in Hong Kong, the existing candidate
vaccines could expedite the availability of a new vaccine. The candidate
prototype vaccines have already undergone basic tests to ensure safety and
effectiveness, genetic stability, and antigenic homogeneity.
Several steps are needed before a new influenza vaccine is ready for use in
humans. Virus for use in influenza vaccines is grown in chicken eggs.
However, because H5N1 is so deadly in chicken embryos, a new technique,
known as "reverse genetics," is required to prepare the prototype H5N1
virus for vaccine production. Reverse genetics merges selected genetic
information of the virus taken from actual cases with a laboratory virus.
The resulting virus is recognized by the human immune system and causes a
protective immune response but no disease. The virus can also be
genetically modified so that it is no longer lethal to chicken embryos. As
a further advantage, use of the reverse genetics technique produces a
prototype virus with predictable growth during vaccine production.
The prototype virus is then used by manufacturers to produce sample
vaccines for clinical testing. WHO will offer support in the coordination
of these clinical trials, which are needed to determine the amount of
vaccine and number of doses required to confer protection, also in
different age groups.
As part of its influenza pandemic preparedness plans, WHO also has in place
procedures for making specific recommendations to vaccine manufacturing
companies and licensing agencies for the composition and approval of a
vaccine during an influenza pandemic.
The WHO Global Influenza Laboratory Network was established in 1947 to
guide the yearly composition of influenza vaccines. The oldest disease
surveillance network at WHO, it also operates as an early warning system
for detecting conditions -- including novel viruses -- that could give rise
to another influenza pandemic. Historically, influenza pandemics have
spread rapidly around the world, causing high mortality and affecting all
age groups, including young and healthy adults. The most severe pandemic in
the previous century, in 1918-1919, killed an estimated 50 million persons.
--
Marianne Hopp
<mjhopp12@yahoo.com>
See Also
Avian influenza, human - Vietnam (08) 20040119.0216Avian influenza, human - Vietnam (07) 20040119.0213
Avian influenza, human - Vietnam (06) 20040118.0193
Avian influenza, human - Vietnam (05) 20040117.0181
Avian influenza - Eastern Asia (02) 20040116.0176
Avian influenza, WHO fact sheet 20040116.0171
Avian influenza, human - Vietnam (04) 20040114.0155
Avian influenza, human - Vietnam (03) 20040114.0154
Avian influenza - Eastern Asia 20040114.0145
Avian influenza, human - Vietnam (02) 20040113.0138
Avian influenza, human - Vietnam: RFI 20040112.0127
Avian influenza - Japan (02) 20040112.0125
Avian influenza - Japan: RFI 20040111.0124
Avian influenza - Vietnam (02) 20040110.0106
Avian influenza - Vietnam: OIE 20040109.0101
Avian influenza - Thailand (02): not 20040109.0097
Avian influenza - Thailand: RFI 20040105.0051
Avian influenza - Eastern Asia 20040114.0145
Avian influenza - Eastern Asia (02) 20040116.0176
Avian influenza - Eastern Asia (04): RFI 20040119.0208
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