How Effective Are Bird Flu Vaccines?
2007-03-26 23:16阅读：
How Effective Are Bird Flu Vaccines?
Avian Flu | China | Thailand
By Li Hujun, Southern Weekly, Beijing bureau
China has implemented the compulsory immunization of poultry with
government-funded vaccines since the end of 2005. Unfortunately,
the weakest link in China's system for preventing animal epidemics
still lies at the grassroots level.
(Photo Caption) Mr. Jin’s duck farm is very close to
Gao’s hennery, and the ducks were not closed. All ducks in Jin’s
farm were vaccinated. However, according to a Hong Kong-US joint
research, about 3.3% of ducks in Yunnan and other Southern
provinces were H5N1 positive.
(Photo Caption) The price of this gamecock is as high as
100, 000Bahts(more than 2,600 USD). In Thailand, the
vaccination is illegal.
Gao Wenbin’s hennery got attention from the State
Council.
In November 2005, more than 2,000 chickens in Gao's poultry farm
in Lotus Village of Chuxiong city, Yunnan pro
vince was wiped out by the deadly H5N1 bird flu virus. The incident
prompted special visit and inspection from Vice Premier Hui
Liangyu.
Gao had no idea how the chickens caught the virus. He bought
over 10,000 chicks and injected them with bird flu vaccines
manufactured in Inner Mongolia. The vaccines, however, did not have
the Ministry of Agriculture license, so they were deemed as
sham.
Now, all the chickens in Gao’s farm have been injected with
genuine vaccines provided free by the town's veterinary
clinic.
Are these vaccines able to resist avian flu virus?
HIDDEN DANGER
In the one year following poultry deaths in Gao’s farm, there
wasn’t any public report on bird flu pandemic in Yunnan. However,
calmness on the surface does not mean risks from avian flu have
been eliminated.
On Oct. 30, 2006, a research team led by Guan Yi, director of
the State Key Laboratory of Emerging Infectious Diseases at the
University of Hong Kong, and Rob Webster of St. Jude Children's
Research Hospital in Memphis, United States, published a study in
the U.S. journal Proceedings of National Academy of
Sciences.
The team collected over 50,000 samples from poultry markets in
six southern Chinese provinces including Yunnan, and found the rate
for H5N1-positive chickens, ducks and geese was 0.5, 3.3 and 3.5
percent respectively.
The team claimed that they first detected a new Fujian-like
strain of the H5N1 virus in March 2005, and this type of virus had
already been transmitted to Hong Kong, Laos, Malaysia and Thailand.
After analyzing some samples of chicken blood serum, the team
observed that the bird flu vaccine China now uses was not effective
for the Fujian-like breed. They also inferred that large-scale
vaccination might, in fact, facilitate the gradual dominance of the
Fujian-like virus.
The direct challenge that this study posed to China's compulsory
immunization policy led the Ministry of Agriculture to fiercely
criticize the article.
Jia Youling, China’s chief veterinary officer with the Ministry
of Agriculture' Bureau of Animal Health, appeared at a press
conference hold by the State Council Information Office. He accused
Guan Yi and his colleagues of unlawfully obtaining samples and
questioned the reliability of the team's data and rejected its
conclusions.
The World Organization for Animal Health (OIE) and the United
Nations Food and Agriculture Organization (FAO), meanwhile, issued
a joint statement saying the research team's conclusions would not
be too surprising if they were verified, because avian flu viruses,
after all, are known to mutate fairly quickly.
While Guan Yi said, “We have kept all the original samples for
our data. They could come and check on it. This year, we had a much
higher rate of viruses detected from poultry samples than last
year. Why is this? Many bird flu patients in China were infected
with the Fujian-like strain. Although at the moment chickens are
not dying, what if people start to die?”
Jia Youling also revealed that the national veterinary services
tested 305,000 pathogenic samples from poultry and wild birds
during past ten months. Among poultry samples, 25 turned out to be
positive for bird flu, all of which came from Yunnan and two other
provinces.
An expert who prefers to remain anonymous noted: “Although there
are fewer public reports on the pandemic, it doesn’t mean that we
could pay less attention to avian flu prevention.”
Up to the end of November 2006, 21 people had tested positive
for bird flu in China. Of this figure, 14 had died. Worldwide,
there had been altogether 258 human bird flu cases, with 154
deaths.
Nonetheless, Ms Wang, a villager living near Gao Wenbin’s
poultry farm, still does not know that bird flu has already caused
human deaths.
UNATTAINABLE TARGET
Under the government’s seemingly lax strategy on bird flu, the
role of vaccination has been placed at an unprecedented high
level.
Li Jinxiang, deputy chief of the Bureau of Animal Health, once
pledged at a press conference an average vaccination rate of over
98 percent for poultry in the country by June 2006.
In reality, that’s a very difficult target.
Song Xuelin, head of Yunnan Provincial Veterinary Epidemic
Prevention Station, said only large-scale poultry farms could
achieve the 100-percent vaccination target, and small household
farmers could hardly achieve it. Thus, the bird flu vaccination
rate in the province would stand at over 80 percent higher in more
developed areas and lower in remote regions.
According to him, some villagers were not willing to inject
vaccines to their poultry, for fear of frightening poultry, or
killing the weaker ones. Even if small household farmers were all
willing to take vaccination, there are few people or resources to
do the job. “Once you have the bullets, you still need to shoot,”
he added.
Nonetheless, with the compulsory vaccination policy in China,
bird flu vaccines have become a profitable industry. But how was
its effect?
Chen Hualan, director of China’s National Avian Influenza
Reference Laboratory, said that existing vaccines can protect
waterfowl from the virus in southern China quite well, up to almost
100 percent even. She based her observation from laboratory
experiments she has done in her laboratory.
However, vaccines are not always so effective. In Chuxiong city,
Yunnan Province, the success rate for antibodies against bird flu
at the end of 2005 was 93 percent.
Prevention results in autumn 2006 were even less ideal. For
instance, the Chuxiong Veterinary Epidemic Prevention Station
ordered a vaccine for both bird flu and Newcastle disease, a type
of disease that causes mild conjunctivitis and flu-like symptoms in
birds. The antidote had been developed by Chen Hualan’s
lab.
However, surveillance results gave Li Chaocang, deputy chief for
Chuxiong Vet Station, a fright. The results showed only a 14
percent success rate for bird flu antibodies, with some farms
having a zero pass rate.
Out of frustration, the Chuxiong Vet Station had to use a
vaccine solely meant for avian flu all over again, with a final
antibody pass rate of 72 percent. Li quoted experts from provincial
level as saying that there was no problem with the joint vaccine
itself. Something might have gone wrong when farmers carried out
the vaccination, he added.
Prof. Bi Yingzuo from South China Agriculture University said he
could not comment since he did not know much about the exact
circumstances around the Chuxiong incident. However, he added,
immunization is not a one-jab thing. The processing of the
vaccines, animal susceptibility and careless immunization practices
could all affect the outcome of the exercise. Clearly, the lack of
technical support in the grassroots level is a major
factor.
In China, a village veterinarian plays a key role in the
prevention of a bird flu pandemic. However, Ms. Yang Ke, a
technician working for Ziwu Town vet station said, 'In places where
vaccination is well conducted, there are fewer animal diseases,
which means the income of a vet would decline. Therefore, some vets
are not very responsible as expected. They might just use a syringe
and pretend to inject.”
Lack of technical support and poor pay are juts the tip of the
iceberg. According to Song Xuelin, vets are poorly paid and not
skillful enough despite increased government support in the last
few years.
Yang Peichang, head of the Chuxiong Vet Station, is extremely
concerned about the vets’ professional qualifications. “The staff
at our station is ageing. While the manning quota is full, new
college graduates could not get in. On the other hand, people
unqualified for the job have been squeezed into vet stations as an
undesired result of township institutional reform.”
THAI STRATEGY
Among the Mekong countries, Vietnam is also doing avian flu
vaccinations on a large scale. According to Dr Jeffrey Gilbert,
avian flu senior technical coordinator for the FAO in Vietnam, a
vaccination drive was launched in Vietnam with FAO support, and it
is estimated that 99 percent of the vaccines were from the
well-reputed Chinese Institute.
Apart from close cooperation among communities, Gilbert said
continued surveillance of all poultry is of vital importance.
“People need to understand how the virus spread in vaccinated or
unvaccinated poultry and whether mutation has taken place. It is
also important to ensure vaccinated birds develop resistance
against the virus.”
In sharp contrast, Thailand, another country in the Mekong
region, has completely banned bird flu vaccines.
Prof. Porntep Ratanakorn of Mahidol University,
believes that whether a country carries out vaccination or not
depends on various elements, be it political, economic or
technological. One general concern is how vaccination would affect
the export of poultry products. Hence, Thailand has put more
emphasis on measures other than vaccination to prevent bird
flu.
In a gamecock farm in Chiang Saen village, Chiang Rai of
northern Thailand, hundreds of gamecock are separated from
each other by barbed fenced, and they have enough space to roam in.
Doi, the owner of the farm, said a clean environment is vital for
gamecocks to develop better resistance to diseases.
Doi has been in the trade for over 30 years and is quite a
figure in cockfighting circles in northern Thailand. He owns a
gamecock named Ath Het, which is now worth 100,000 baht (2,600 U.S.
dollars). He used to take his gamecocks across the border to
Yunnan, China. However, since the outbreak of bird flu three years
ago, China has stopped allowing live poultry to cross its
borders.
Although Chiang Rai province hasn’t witnessed any bird flu
epidemic, the rule in Thailand is for every gamecock to have a
“passport” if it fights in another province, an important
managerial method on migrating poultry.
Duck King is a duck company located in central Thailand. It
practices enclosed farming, which keeps the ducks away from direct
contact with people and other fowls. Samples are collected every
eight weeks for local vets to check.
According to Anant Singhattha, a local veterinary
officer, the number of poultry farms had dropped from 1,200 to 430
since bird flu broke out in Thailand in 2004. Those without
bio-safety measures were all closed down. What's more, government
orders that poultry farms should be at least five km away from each
other.
Dr Supamit Chunsutiwat, senior expert for
Thailand’s Health Ministry on disease control, referred the five km
distance policy as “compartment”, and it was a new measure in the
country’s bird flu prevention. “As to its effect, it might not be
clear until five to ten years later,” he added.
A non-governmental organization, Kenan Institute Asia, has been
engaged in school education on avian flu prevention in Thailand.
James Hopkins, head of the program, said relevant textbooks have
been dispatched to 40,000 schools in the country. “This is the
first time that a specific public health training textbook was sent
out to every school,” he added.
After the Sep 19, 2006 coup in Thailand, there had been renewed
discussions on whether the country should follow China’s
immunization policy. One group favors vaccinating gamecocks that
traveled long distance and free-range poultry without bio-safety
measures to reduce the risks of bird flu transmission.
Hopkins is planning to conduct a forum on the prevention
of cross-border bird flu among the Mekong countries, “some
countries don’t want to publicize the avian flu epidemic,
preferring to deal with it internally. But bird flu is no longer a
country’s internal affair. Every country has to share information
and work together.”
LASTING STRUGGLE
Bird flu prevention has become a long-lasting struggle.
Vaccination, said Song Xuelin, is not the only preventive measure.
There are, after all, different kinds of bird flu and viruses are
constantly mutating. One vaccine could only target one virus.
Therefore, improving hygiene and managing enclosed poultry farming
are both very important.
Both the OIE and FAO, meanwhile, regard vaccination as one of
the measures for bird flu control. The two groups also stressed on
disease monitoring and surveillance after vaccination, apart from
improved hygienic practices in the farm and efficient management of
poultry transport.
However, in Chuxiong, Yunnan Province, prevention measures are
not satisfactory even in large-scale farms. At Gao Wenbin’s farm,
dozens of chickens still roam out of the enclosed area and stroll
in front of the dorms of the farm staff. The air reeked of chicken
feces. Dozens of meters away is Old Jin’s duck farm where over
2,000 ducks were raised in the open air, many of them playing in a
pond nearby.
In a report on bird flu prevention, Chuxiong Animal Husbandry
Bureau advocated a change in poultry farming to scale farming. But
Li Haifen, head of the vet section in the bureau, said so far no
concrete measures have been mapped out.
In contrast, the monitoring of avian flu in humans is much
better. Since vaccines for human bird flu cases have yet to be
developed, the health sector has no recourse but to rely more on
the monitoring system.
Though there has not been any human bird flu case in Yunnan, the
Provincial Centre for Disease Control and Prevention (CDC) director
Lu Lin revealed that a preliminary flu and human avian flu
monitoring network have been set up, and several hospitals have
been collecting samples all year round.
In Yunnan, the provincial health and agriculture departments
have initiated a new response mechanism in the wake of a bird flu
epidemic, under which the two departments would intervene, report
and deal with the pandemic simultaneously.
Lu noted that transparency is a must. Even if only one or two
free-range poultry are suspected of carrying the virus, the health
department should be notified immediately. “If the health
department was notified only after someone got infected, it would
be too late.”
(Li Hujun wrote this story under the Avian Flu Series of the
Imaging Our Mekong program, 2006-07, coordinated by IPS
Asia-Pacific and Probe Media Foundation Inc. The story was
published by Southern Weekly on Jan. 11, 2007.)
