December 29, 2005
Expert: Bad vaccines may trigger China bird flu
By Tan Ee Lyn
HONG KONG -- 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.Thirty-one counties in China have reported outbreaks of the 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 both."
Webster praised China's ambitious plan to vaccinate all its chickens, but also called for agricultural vaccines to be standardized.
"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 million people.
"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'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.