Four hundred global experts on all aspects of the H5N1 strain of the highly pathogenic avian influenza virus (HPAI) met in the Italian city of Verona on 20-22 March 2007 for a conference entitled, ‘Vaccination: a tool for the control of avian influenza’. The meeting was organised jointly by the World Organisation for Animal Health (OIE), Food and Agriculture Organisation (FAO) and Istituto Zooprolifattico Sperimentale delle Venezie (IZSVe) and it was supported by the European Commission. The high levels of both organisers and participants demonstrated how seriously the world is taking the disease. In the current series of outbreaks since 2003, 50 countries have reported outbreaks of the disease – with most countries in Asia, Europe, Africa and the Middle East affected for at least a period of time. Of the 281 known cases of the virus infecting humans, 169 patients had died as the conference was taking place. The global poultry industry and international trade have already suffered significant setbacks.

Vaccination against HPAI was much used in the 1980s and early 1990s, although it was controversial even then. This was followed by a period with a general policy against vaccination but the early years of the new century brought many emergency situations and the international community began again to consider the use of vaccination as a method to control the emerging pandemic.

The case for vaccination

The location of the meeting was not coincidence, as Italy was struck by a previous round of HPAI from 1999, so the hosts were in a position to describe their own experiences. The Italian turkey industry was hit by several waves of the virus before it was finally eliminated. As she mentioned in the abstract of her paper, Dr Ilaria Capua of the IZSVe reminded the audience that vaccination against AI is a recommended tool to control the disease: it is known to increase the resistance of susceptible birds to infection and to reduce the number of viruses shed. It is important to recognise, however, that vaccination does not necessarily prevent infection, leaving vaccinated and infected flocks as a potential source for the perpetuation of infection.

In order to reduce the spread of infection in infected flocks, it is essential that vaccination strategies are implemented to enable ‘Differentiation of Infected from Vaccinated Animals’ (DIVA), Dr Capua asserted. This requires monitoring after vaccination so that vaccinated and exposed flocks can be identified and subjected to controlled marketing.

Types of vaccines

Several different types of vaccines against AI are available: these may be live or inactivated, homologous or heterologous. Homologous vaccines are made from the same strain as the pathogenic one circulating, i.e. H5N1 currently. Whilst offering theoretically the best protection, this type of product rules out the possibility of using the DIVA principle, since infected birds cannot be differentiated from vaccinated ones. Some examples of commercial vaccines are given in the table.

Some of the poultry vaccines used in the current outbreaks of H5N1

Product name

Company

Vaccine strain

Species

Nobilis Influenza H5

Intervet

H5N2

chickens

Trovac AIV-H5

Merial

H5

chickens

-

(China)

H5N2

chickens

Poulvac FluFend H5N3 RG

Fort Dodge

H5N3

chickens, ducks

Gallimune Flu H5N9

Merial

H5N9

ducks

-

Weike-Harbin (China)

H5N1

waterfowl

Bivalent vaccines:

 

 

 

BioFlu H7N1-H5N9

Merial

H7N1, H5N9

 

Poulvac I AI H5N9-H7N1

Fort Dodge

H5N9, H7N1

 

Note: This is not an exhaustive list; the list of approved products for the different poultry species varies between countries.

There has also been activity to develop a combined vaccine, offering protection from AI and another disease, for example, Newcastle disease.

Countries and regions differ widely in the regulatory status of AI vaccines, and whether they are tested and approved for the various different domestic poultry species.

Locally manufactured vaccines are used widely in China and other parts of Asia, often on grounds of cost. At the Verona meeting, the delegate from China announced that the country was to change its policy and to start using a locally produced homologous vaccine in the next round of vaccinations.

On vaccines, several speakers emphasised the vital importance of a certified cold chain to supply vaccines to farm/village level. More information is needed on the useful life of the vaccine if that cold chain is broken.

There was a repeated call for vaccines to be available in smaller bottles more suitable for regions of small backyard flocks.

The case for stamping out

 Among the disadvantages of vaccination are its high costs in terms of the vaccine itself and the time and manpower needed to carry it out. The procedure is cumbersome and labour intensive. For housed flocks, it can be both effective and worthwhile but the logistics of catching and vaccinating all the domestic poultry in an isolated village should not be underestimated, even where labour is relatively cheap and plentiful.

Local veterinary services

Where local veterinary services are scarce or non-existent, as is the case in many parts of the developing world also poorly served by medical personnel, there is little hope of providing control of HPAI without significant intervention from international agencies. Effective control of the disease cannot be achieved without an adequate number of trained veterinarians in the region.

Questions of compensation

The topic of the correct form of compensation to farmers whose flocks have been culled was raised several times, including a full paper by Brian Bender of the World Bank. Learning from past experience, his organisation is in a constant state of preparedness to financial payments to poultry farmers whose livelihood is wiped out when their flocks are infected or near to an outbreak. Compensation is not made for subsequent losses as the result of price drops or international trade bans but only for culled birds. Identification of the payee can be fraught with difficulties in cases where birds are owned by and grown under contract for large integrators. Small commercial farmers and those with backyard flocks need and deserve support but how to do that most effectively? Mr Bender stressed the need for urgent action - payments within 48 hours of culling should be the target – in order to minimise the hardship. The levels of compensation differed widely between countries, depending on the incentive required to get producers to report possible disease outbreaks promptly.

Financial recompense can be most difficult to administer in remote regions and tends to attract corruption. Delegates mentioned how farmers had been offered some type of voucher for more chicks and/or feed in some countries, with success. There is a real danger, however, that farms are re-stocked while the virus is still in the area, leading o cycle after cycle of disease breakdown. A suggestion to link the voucher to training on biosecurity and the supply of sanitation equipment has a great deal to recommend it.

Summing up

Experience teaches us that vaccination is a powerful tool in the control of HPAI in poultry. However, as Joseph Domenech (FAO chief veterinary officer) emphasised, it cannot, on its own, conquer the disease. Other control measures, including heightened biosecurity and close monitoring of the situation, are essential to stop the spread of the disease.

The decision on the use of vaccination or not depends on local circumstances. When outbreaks are isolated and the virus has only been identified in wild birds, strategic culling is an appropriate strategy, whereas vaccination combined with culling of infected flocks is the answer where the disease has – or threatens to - become endemic. There may be good reasons to make exceptions, however. In the Netherlands, for example, small free-range flocks belonging to hobby farmers have been granted an exemption and have been vaccinated. This was considered preferable to forcing owners to keep their birds housed during prolonged periods of high HPAI risk from migrating wild birds.

Among the many recommendations arising from the conference are that the objectives of any vaccination strategy should be defined before vaccination is implemented in a country or region.

International co-operation is also vital. A new agency, OFFLU, has been set up by the OIE and FAO to gain understanding of the movement of the virus. The same agencies with WHO have set up GLEWS (Global Early Warning System) for all types of emergency including HPAI. It is vital that countries suspecting an outbreak of H5N1- be it highly or low pathogenic type - should inform the international authorities at once and share openly whatever resources and knowledge they have with the international community. There is no shame in this: HPAI has become a serious global problem that threatens human lives and livelihoods and it will require all our efforts to eliminate it.

As Mr Domenech remarked, “Tackling AI requires a holistic approach, taking into account farming systems, biodiversity, livestock production and movements as well as socio-economic factors.”