Four considerations in the discussion whether to vaccinate against bird flu

February 8, 2021

Every year, bird flu is transmitted to poultry farms in the Netherlands and elsewhere. And every time, the question arises: should we or shouldn’t we vaccinate against bird flu (avian influenza)? The answer is not as straightforward as the question. The discussion has many aspects, which Wageningen University & Research lists below.

1. Is a vaccine for avian influenza available?

In the Netherlands, only one commercial vaccine is available and registered for use on poultry. This vaccine is based on a low pathogen avian influenza (LPAI) type H5N5 strain from 1986. This vaccine strain is not compatible with the current high pathogen avian influenza (HPAI) H5N8 virus. It is thus expected to provide insufficient protection against this viral infection.

There are several other commercial vaccines against H5-viruses available abroad. Still, none of these vaccines has been developed to combat the HPAI H5N8 virus currently causing outbreaks in the Netherlands. (Update 2022: also not against the current H5N1 virus.) If a vaccine only partially protects poultry from infection with avian influenza, this could result in the disease remaining undetected, thus allowing it to spread unchecked. This makes it more difficult to control. 

2. Is poultry in other countries vaccinated?

Poultry in several countries (in Asia, Egypt) is being vaccinated against bird flu, HPAI H5, among others. A vaccine must primarily be directed against stopping the spread of the virus and preventing outbreaks (lowering the transmission to R<1). Lab tests have shown that vaccines can prevent the transmission of the HPAI virus if the vaccine strain and the outbreak strain are closely related. In practice, however, it transpires that too few antibodies for the HPAI virus are generated after one or two inoculations. Thus, the developed vaccines were not sufficiently effective in the field (R>1) and were unable to prevent outbreaks in these countries.

3. What conditions should a vaccine against avian influenza meet?

  • The vaccine should provide adequate protection from an infection with the bird flu, and prevent the spread of the virus. However, developing an effective vaccine is far from easy, as the HPAI virus mutates and evolves rapidly. So far, no vaccine that protects against all strains of avian influenza has been developed. Therefore, a vaccine must be continually altered for the specific strain of the virus causing outbreaks at that time.
  • A vaccine must also be suited for mass vaccination of poultry, for example through a spray or via the animals’ drinking water. A vaccine that must be administered to each animal individually is labour (and, therefore, cost) intensive.
  • Finally, the inoculated animals must be distinguishable from infected animals in diagnostic tests. After vaccination, animals develop antibodies to the virus, much like animals that have been infected. To seek out the infected animals, the vaccine must have a distinguishing characteristic. This principle is known as the DIVA principle (Differentiating Infected from Vaccinated Animals).

4. In addition to developing a vaccine, what else must we consider?

At this time, the European Union disallows trading of vaccinated poultry (products). Other countries are generally also wary of importing vaccinated poultry (products). If the Dutch poultry farmers wish to vaccinate their animals, this could have severe implications for export. International agreements are needed on vaccination and acceptance of vaccinated poultry (products).

As a result of the trade restrictions, there is currently no market for bird flu vaccines in the EU, making it unprofitable for the pharmaceutical industry to develop a vaccine. But, it is precisely the lack of an effective vaccine that prompts countries to maintain their trade restrictions, because they consider the risk of importing unidentified infected poultry too great.

The risk of HPAI occurring in the next few years is considered high. Thus, this would be the time to discuss vaccination at a global level and invest in the development of an effective vaccine. A vaccine strategy is an essential consideration in this regard. Possibilities are preventive inoculation of all poultry, or more targeted vaccination when HPAI outbreaks occur or are expected to occur.