Extract from ProMed post  March 19 2006 
[3] China, HPAI vaccines and silent excretors
Date: Sat, 18 Mar 2006
From: ProMED-mail <promed@promedmail.org>
Source: Reuters, 17 Mar 2006 [edited]

The discovery in southern China of healthy-looking chickens that are infected
with the deadly H5N1 bird flu virus has raised fears among experts that
vaccines used in the country are substandard.

Bad vaccines for poultry can "mask" diseases. The vaccines protect birds,
which often don't show symptoms, but do not guard against infection and the
birds can shed the virus in their faeces.  The virus then spreads to more
birds, mutates and can even jump species barriers, for example, into humans.

In a 2004-2005 survey, researchers found seemingly healthy but H5N1-infected
chickens in poultry markets in south China, including Guangdong, just north of
Hong Kong.

The development is unsettling. Chickens usually die within 24 hours of being
infected with H5N1, but without signs of disease the virus is harder to
detect, control, and also much easier to pass on to unsuspecting humans.

The risk of such asymptomatic poultry came to the fore earlier this month when
a man died in Guangdong after visiting several live poultry markets and
officials later said he probably caught the disease from live but H5N1-
infected birds.

Experts are now asking hard questions about the quality of China-made vaccines.

"With this finding of asymptomatic birds, we have to ask if this is because of
the vaccines they use, a mutation of the virus? The issue of vaccines has to
take top priority," said Hong Kong infectious disease expert Lo Wing-lok.

The World Health Organisation, which backed China's plan to vaccinate billions
of poultry in 2005, is also concerned.  Julie Hall, in charge of the WHO's
outbreak response in China, said recently that studies were needed to see if
China's vaccination programme might be "masking" the virus, which has killed
about 100 people in Asia and the Middle East since 2003.

China's Harbin Veterinary Research Institute, which is linked to the Ministry
of Agriculture, makes flu vaccines for poultry. The ministry approves these
vaccines and controls their sale and distribution.

"Because information is not abundantly available, there is speculation the
vaccines may not be as effective.  It is up to the Chinese authorities to be
more transparent," Lo said. China's Ministry of Agriculture (MOA) has declined

An expert familiar with the situation said: "MOA is the only place allowed to
develop, manufacture and distribute vaccines. It is not the best vaccine. It
can save the bird's life but it can't stop the virus from replicating. The
bird looks good, but it has the virus. If you bring it into an unvaccinated
area, other birds die and people (who contract the virus) die," the expert

"Places like Vietnam and Thailand are importing these Chinese vaccines. So
what is happening in China (asymptomatic poultry) can happen in these places
soon," said the expert.

But Vietnam, which has had no new bird flu outbreaks in poultry or humans
since November 2005, is not overly worried. It says the China-made vaccines
must pass quality-control tests.  "We have been using Chinese vaccines
nationwide and there has been no problem regarding quality," said Hoang Van
Nam, deputy director of the Agriculture Ministry's animal health department.
"We have just completed tests of 20 000 poultry nationwide and found no trace
of bird flu," Nam said. Neither has the department found any asymptomatic

Although Thailand bans H5N1 vaccination in chickens, there have been reports
of police seizing vaccines being smuggled along the Mekong River from China.
But nobody knows if they have been smuggled in successfully and used.

Although China has been vaccinating its farmed poultry in the past few years,
that has not stopped the virus from proliferating and mutating. After
scientists first isolated H5N1 in a goose in Guangdong in 1996, the virus has
continued brewing and there are now 5 dominant subtypes in southern China.

In the past year, H5N1 has spread across 14 Chinese provinces and regions, and
penetrated parts of the Middle East, Europe and Africa after infecting many
parts of Asia since late 2003.

Although migratory birds probably carried the virus from China's Qinghai Lake
to Africa and Europe, microbiologist Guan Yi from the University of Hong Kong
believes that the spread of the virus in southern China is due largely to
domestic poultry.  "The virus outbreak in south China is not caused by
migratory birds, but domestic ducks and geese and maybe chickens," he said.

Guan, whose laboratory has genetically sequenced strains of the virus found in
many parts of the world, believes live poultry exports from southern China
probably introduced the virus into Vietnam, Thailand, Malaysia and Indonesia.

[Byline: Tan Ee Lyn]


[The paper in PNAS describing the discovery of H5N1 viruses in some apparently
healthy chickens in live-bird markets in southern China was presented and
discussed in posting 20060212.0468 (see there: [5] China - H5N1 multiple
sublineages). Reservations regarding some of the paper's conclusions were
later expressed by Les Simms (see [2] in 20060218.0536).  Dr Guan Yi's
concerns about the possible role (deficient) vaccines may have played in the
creation of silent excretor chickens and the maintenance of H5N1 in China and
elsewhere were included in a previous post (see [4] China, subclinical
infection: chickens, ducks and geese; in 20060310.0761).

The quality of veterinary vaccines is a crucial factor in controlling
infectious diseases, avian influenza certainly not excluded. The Vietnamese
observations are significant, indicating that the issue is not simply the use
of vaccines, but their quality. When bona-fide, certified, safety-and-efficacy-
tested vaccines are used, the results do not disappoint. Wide-scale
application of uncontrolled vaccines, produced in uncertified plants, may
indeed lead to disastrous outcomes. China seems to have recently recognised
the problem and undertaken the complex task of improving controls on its
vaccines; early implementation is most desirable. - Mod.AS]