Detection | Vaccines | Prevention | Preparation | Recommendations

Definition of a Vaccine

A vaccine can in simple terms be explained as a substance that prevents virus infection and the disease it causes. However, on more technical terms, the Food and Agricultural Organisation of the UN defines a vaccine as "a preparation of dead or weakened pathogens, or of derived antigenic determinants, that is used to induce formation of antibodies or immunity against the pathogen."

Human Bird Flu Vaccines

As of date, no vaccines exist for avian influenza in general. There is currently research underway to develop a vaccine against the H5N1 and H9N2 bird flu viruses, but a novel virus which could trigger a global pandemic is ultimately the disease for which a vaccine is needed. The largest problem is that the vaccine for whatever new subtype emerges cannot actually be created until scientists have a sample of that virus, making the situation rather difficult. Furthermore, current estimations for vaccine production stands at 4 months, much too long if a pandemic were to arise.

Vaccine Development and Production

Various experimental vaccines, primarily targeting the H5N1 virus subtype have been developed since 2004, but unfortunately have not produced any successful results. Heavy research has been undertaken by various universities and development centers across the globe to come up with a polished product. However, no licensed vaccines for human usage exist as of yet.



The National Institute of Allergy and Infectious Diseases (NIAID) of the US was last reported on August 6, 2005 to be partially successful in the preliminary trialings of a candidate vaccine for H5N1 in healthy adults. Excepting that an excessive dosage (12 times the quantity of an average seasonal influenza vaccine) was required to yield positive results, the vaccine did provide immunity. Meanwhile the National Hygiene and Epidemiology Institute (Vietnam) was awaiting government and WHO approval to run human trials in mid November 2005 on a vaccine successful in chickens and monkeys.

Vaccination trials are separated into phase I and phase II trials, testing first for safety and ability to stimulate immunization in healthy adults, then testing for its effects on the young and the elderly.

** Update: A number of H5N1 vaccines are now in their latter stages of clinical testing and are expected to be available for stockpiling sometime in 2007. The UK drug firms GlaxoSmithKline announced in July 2006, that they had successfully developed a vaccine which had passed clinical trials. Relatively small doses of the vaccine provided sufficient immunity to H5N1, making it commercially feasible for production. Furthermore, the Microgen Centre in Russia is also anticipating its pilot vaccine to be ready for mass production in March - April next year.

The major concern remains however, that the vaccines produced may not be effective against new strains of H5N1 since they are based on current H5N1 strains. In the event of a global pandemic though, it would likely be caused by a novel strain, possibly rendering vaccinations useless. However, immunizations against current bird flu viruses will nonetheless prevent human contraction from poultry and should therefore reduce the likelihood of mutation.

Use of Normal Flu Vaccines

Although no human vaccines are currently available to protect against the H5N1 strain of virus in Asia at this point in time, seasonal influenza vaccines are recommended to be received by those most likely to contract bird flu (poultry farmers, cullers etc.). By preventing seasonal influenza, risks are reduced that bird flu and seasonal flu are simultaneously contracted within one patient. Simultaneous virus contraction could potentially allow virus mutation to occur and make way for the creation of a novel strain.

AI Vaccines for Poultry

Vaccine injections are available for chickens and turkeys to provide immunity against bird flu. However, different injections must be administered to target different subtypes of virus, making it difficult and also costly to immunize whole populations of poultry. Vaccination is thus usually a supplement to poultry culling in order to stop disease spread once the virus has been identified. At present, there are two different types of vaccine available – inactivated oil emulsion vaccines and a recombinant fowl pox vector vaccine.

The inactivated vaccine consists of previously virulent bird flu viruses that have been killed but still trigger immune responses in the body. These vaccines require a booster shot to maintain the effect. The recombinant vector vaccine combines the physiology of the fowl pox virus with the bird flu gene that triggers H5 antigen production to create immunity against avian influenza. These vaccines are however, only effective for their own subtypes of bird flu and no one vaccination is currently able to provide immunity for more than one subtype.

Effectiveness of Poultry Vaccines

Even vaccinated chickens and turkeys are not 100% immune from disease, especially since such a variety of subtypes exist. It’s been found however, that those particular birds which contract bird flu even after receiving vaccination, often shed much less virus during infection than otherwise, lowering the risk of rapid spreading. However, culling remains the most effective way of controlling bird flu epidemics and vaccines are commonly supplementary.