December 29, 2005
Bad vaccines may trigger China bird flu-expert
By Tan Ee Lyn
HONG KONG (Reuters) - China is most likely using
substandard poultry vaccine or not enough good vaccine, which
would explain recent outbreaks of the deadly H5N1 bird flu
virus in poultry, a prominent virologist said on Thursday.
H5N1 in poultry this year, although only one county remains
under isolation and there have been no new outbreaks for three
weeks, according to Chinese state media.
But the fear among experts is that the virus could mutate
from a disease that largely affects birds to one that can pass
easily between people, leading to a human pandemic.
Dr Robert Webster, of St Jude's Children's Hospital in
Memphis, Tennessee, said the problem of substandard vaccines
was not exclusive to China.
"If you use a good vaccine you can prevent the transmission
within poultry and to humans. But if they have been using
vaccines now (in China) for several years, why is there so much
bird flu?" Webster told Reuters in Hong Kong.
"There is bad vaccine that stops the disease in the bird
but the bird goes on pooping out virus and maintaining it and
changing it. And I think this is what is going on in China.
"It has to be. Either there is not enough vaccine being
used or there is substandard vaccine being used. Probably
Webster praised China's ambitious plan to vaccinate all its
chickens, but also called for agricultural vaccines to be
"It's not just China. We cant blame China for substandard
vaccines. I think there are substandard vaccines for influenza
in poultry all over the world," he added.
Since late 2003, there have been 141 confirmed human cases
of the deadly H5N1 strain of bird flu, all of them in Asia,
including six in China. Two people have died from bird flu in
China, out of 73 known fatalities in Asia.
Webster warned against underestimating the virus, which he
said has exhibited some of the worrying characteristics of the
Spanish flu virus of 1918-1919, which killed an estimated 50
"If you go back to 1918, it showed that there are about 10
critical amino acids in that virus that seemed to be necessary
(for the virus) to be pathogenic," Webster said.
"Many of those changes have been seen in the H5N1, but not
all together. Individually, these have been out there.
"If you get all of these 10 all in together in one (H5N1)
virus, to get 10 amino acids all lined up in the right order,
yes the chances are very, very small that it could happen, but
it could happen you see," he said.
Webster said it was not surprising that some strains of the
H5N1 have been found to be resistant to Tamiflu, Roche AG's
drug that is believed to be capable of reducing the symptoms
and chances of complications caused by the virus.
"That's the nature of the beast, there is nothing special
about this one. Flu viruses change every time they multiply,
they make mistakes, these mutations occur naturally," he said.
It was now crucial to find the cure -- the right doses,
duration of treatments and combining Tamiflu with a few other
anti-viral drugs, such as amantadine and rimantadine.
"It is important to realize that the H5N1 cases in China
recently are also sensitive to the old-fashioned drugs
amantadine and rimantadine. So we need to be thinking more
about combinations of these drugs, combinations of amantadine,
rimantadine and Tamiflu," Webster said.