A United Nations agency will urge wider use of a vaccine among birds to help stop the continuing spread of a virus that is deadly to birds and a threat to human health, an official said Thursday.
The guidelines, to be issued by the end of August by the agency, the Food and Agricultural Organization, are needed because of new findings that the strain of the avian influenza virus has become a permanent fixture in many Asian countries, Dr. Joseph Domenech, chief of the agency's animal health services, said in an interview. Scientists have recently found that the strain of the avian influenza virus, known as A(H5N1), seems firmly rooted among domesticated ducks and wildlife and so cannot be wiped out by culling, quarantines and other standard measures alone, Domenech said.
He spoke at a meeting attended by health officials from 10 southeast Asian countries that Food and Agricultural Organization convened in part to deal with a resurgence of avian influenza in China, Thailand, Vietnam this month and the virus's continuing spread in Indonesia.
An estimated 200 million birds have died from A(H5N1) or culling since early this year when the strain simultaneously appeared in eight Asian countries. The scale of the epidemic of an avian influenza virus geographically, economically and socially is "unprecedented," United Nations officials said. The strain has caused widespread economic havoc to the Thai poultry industry, the fourth largest in the word, and has been costly to the economic and nutritional well-being of many poor people who depend on raising backyard chickens for proper nutrition.
At the same time, many influenza experts and public health officials fear a worst case scenario in which an individual becomes infected with both the A(H5N1) avian virus and a human influenza virus. Under such circumstances, the viruses could swap genes to create a new virus to cause a global epidemic that would be difficult to control.
So far the human toll has been small but virulent. No human cases have resulted from the most recent outbreaks in July. But earlier in the year, A(H5N1) infected 35 humans in Vietnam and Thailand, killing 24 of them. There has been no secondary spread from person to person.
In the A(H5N1) epidemic in southeast Asia, health workers are dealing with a situation that differs significantly from outbreaks of other strains of avian influenza that developed countries in temperate regions have stopped by using vaccines as a short-term emergency measure as an adjunct to culling and other standard measures, said Dr. Mike Nunn who is manager of Australia's Animal Health Science department and Dr. Sarah Kahn, an Australian veterinary consultant to Food and Agricultural Organization.
In February, three agencies, the Food and Agricultural Organization, the World Health Organization and the World Health Organization for Animals, said countries affected by A(H5N1) should consider vaccinations as one measure of stopping its spread.
That recommendation was not as strong as the one expected in the new guidelines because last winter many experts and some countries believed they could eradicate A(H5N1) by culling and making vaccination unnecessary, Domenech said.
Now "we must reassess what we are doing" because of the knowledge that the virus cannot be eradicated due to its presence in ducks and wildlife, Domenech said. "Use of vaccination will be more appropriate than before."
Vaccinations will still be viewed as an adjunct to standard control measures and will require veterinary health workers to carefully monitor what happens to birds, animals and people.
Each country will decide whether to vaccinate against avian influenza. "We are not imposing on them," Domenech said. The vaccines may be appropriate for villages in some countries but not in others, he said. Wherever they are used, the vaccines will not be magic bullets.
Each dose of vaccine costs about five U.S. cents and up to three doses may be needed for each bird. But because the vaccines must be injected, the major cost is from administering them. So an urgent need is for scientists to develop a vaccine that birds and animals can swallow, participants said.
The vaccines are made by killing the A(H5N1) virus. Like most other vaccines, the A(H5N1) vaccines are not 100 percent effective. They protect against symptoms. But a small percentage of healthy vaccinated animals exposed to the virus can still become silently infected and excrete A(H5N1), although in smaller amounts than sick birds.
Scientists believe that the benefits of vaccinating outweigh its risks because the amount of virus that the recipient animal excretes. So the measure "decreases tremendously" the amount of virus that can circulate on farms and elsewhere, Domenech said. But he and other scientists urged health officials to monitor for evidence of potential harm to people. In making such analyses, he said, scientists "must compare vaccinating to doing nothing."
There are two marketed vaccines and Chinese and Indonesian scientists have developed others.
Indonesia has vaccinated 21 million birds, initially using a Chinese vaccine derived from virus isolated in Indonesia, said Dr. Anak Agung Gde Putra, director of regional veterinary laboratories in Bali. Then Indonesia switched to a vaccine made in Indonesia, Agung said. The government is providing the vaccine free to small commercial poultry companies and to subsistence farmers with backyard chickens. Chinese workers are also using the Indonesia vaccine, Agung said. The Indonesian recommendation is that flocks receive two injections of the vaccine spaced about three to four weeks apart.
However, the Food and Agricultural Organization said that significant numbers of vaccinated birds do not show an immune response to the A(H5N1) strain which could mean poor vaccination application or that vaccinating teams missed the animals that were tested.
Thai officials have appointed a committee to study the benefits and risks of using an A(H5N1) vaccine in Thailand.
"Vietnam is almost ready to vaccinate and Cambodia is seriously considering it," Domenech said.