Jan 20, 2004 (CIDRAP News) – The World Health Organization (WHO) said today it is launching an effort to quickly develop a vaccine against influenza A(H5N1), the avian flu virus that has caused at least five human deaths in Vietnam.
The agency didn't predict how long it would take to develop an effective vaccine. But it said two WHO-affiliated laboratories in the United States and Britain developed candidate vaccines for the H5N1 virus last year after it caused two cases and one death in Hong Kong in February.
"If the virus isolated from the fatal cases in Vietnam proves sufficiently similar to the 2003 H5N1 strain in Hong Kong, the existing candidate vaccines could expedite the availability of a new vaccine," the WHO said. The candidate vaccines have already undergone basic tests of safety, effectiveness, and genetic stability.
Yesterday the WHO confirmed the fifth human case of avian flu in Vietnam, involving an 8-year-old girl who died Jan 17 in Hanoi after being hospitalized 2 days. Last week health authorities said four other Vietnamese who had died of a severe respiratory illness had tested positive for influenza A(H5N1), the strain blamed for avian influenza outbreaks in Vietnam, South Korea, and Japan. The Vietnam News Agency said 18 people had the virus and 13 had died.
The WHO has voiced fear that the H5N1 virus could infect a person already carrying another influenza virus, possibly leading to an exchange of genes that could spawn a dangerous new flu virus. Past flu pandemics are believed to have arisen by such mechanisms.
Today's WHO announcement said laboratories in its Global Influenza Surveillance Network are preparing prototype viruses that could be used as "seed stock" for making vaccines. "A prototype virus could be made available to vaccine manufacturing companies within about four weeks," the agency said.
Officials said labs in Hong Kong and Japan have isolated the virus from specimens obtained from two of the Vietnamese patients who died. Lab personnel are analyzing the virus to learn about its origin, assess its relationship to other circulating viruses, and determine its antigenic and genetic characteristics that would have to be incorporated in a candidate vaccine.
The vaccine development effort faces several hurdles, the WHO said. Viruses for use in flu vaccine are normally grown in chicken eggs, but that won't work for H5N1 because it is so deadly to chicken embryos. Consequently, "reverse genetics" will have to be used to prepare an H5N1 prototype.
Reverse genetics involves merging selected genetic material from the natural virus with a laboratory virus, the WHO said. "The resulting virus is recognized by the human immune system, and causes a protective immune response, but no disease." Reverse genetics also permits modification of the virus so that it won't kill chicken embryos.
Manufacturers will use the prototype virus to make sample vaccines for clinical testing, the WHO stated. Officials said the effort to develop a vaccine is in accord with the WHO's 1999 influenza pandemic preparedness plan.
In related news, six scientists from the US Centers for Disease Control and Prevention arrived in Vietnam today to help the WHO investigate how the avian flu has jumped from birds to people, according to Associated Press (AP) and other reports. Fourteen experts in epidemiology, disease surveillance, and animal health will be involved in the investigation, WHO official Bob Dietz told the AP in Hanoi.
Health officials have said they believed the human cases, nearly all of which have been in children, resulted from contact with poultry. No evidence of person-to-person transmission has been reported.
Vietnam's Ministry of Agriculture and Rural Economic Development reported that the avian flu has infected more than 2.3 million chickens and other domesticated birds, out of a total of 245 million, according to a report today by Xinhua, China's official news agency. The ministry has proposed to kill all domestic birds within 3 kilometers of infected sites and is seeking to ban the transport of birds within 10 kilometers of those sites, the report said.
The five deaths that have been clearly blamed on the avian flu virus have been in northern Vietnam, while most of the poultry outbreaks have been in the south. No human cases of the illness have been reported in connection with the avian outbreaks in South Korea or Japan.
The disease has prompted other Asian countries to ban imports of poultry and related products from Vietnam and has dampened plans for the celebration of the Lunar New Year, which begins Jan 22.
Meanwhile, chickens in Thailand have been dying of a disease the Thai government says is fowl cholera and bronchitis, but some farmers believe it is avian flu, according to news reports. A report from Agence France Presse said at least 850,000 chickens have died or been sacrificed because of the disease.
Jan 20 WHO statement on vaccine development plans
Jan 19 WHO statement confirming fifth human case of avian flu