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With losses in the global poultry industry mounting, and concerns over the potential spillover of H5N1 to humans, many countries that until recently have eschewed the use of poultry vaccines are now seriously considering them.
A vaccine that is only partially effective may simply mask the symptoms of infection, but still allow the virus to spread stealthily and continue to evolve. And that is, unfortunately, something we've seen previously:While there are a number of existing H5 poultry vaccines on the market, it isn't known how effective they are against the current clade (2.3.4.4b) of the virus.
Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China).
If we are to proceed down the poultry vaccination road, it is imperative that only highly effective vaccines are used, and that they are properly, and consistently applied.
Today Wageningen University & Research in the Netherlands has announced the preliminary results of a study into the effectiveness of 4 different H5 poultry vaccines.Of the 4, two were found to be 100% effective in protecting chickens against infections (in the lab), while two others fell short.
While encouraging, it will require further testing to determine if they are as effective in the field. This from WUR.
Published on March 17, 2023
Two of the four vaccines tested for their efficacy against HPAI (highly pathogenic avian influenza) type H5N1 bird flu are effective under laboratory conditions. "The so-called HVT-H5 vaccines offer protection against disease symptoms in laying hens and prevent the spread of the virus," said Nancy Beerens, head of the National Reference Laboratory for avian influenza.
The vaccine study was carried out at Wageningen Bioveterinary Research, part of Wageningen University & Research (WUR), in collaboration with Utrecht University, Royal GD and WUR, on behalf of the Dutch Ministry of Agriculture, Nature and Food Quality (LNV).
Vaccines
In the study, three modern vaccines were tested in laying hens. These were:
In addition, the Nobilis vaccine of Merck Sharp & Dome was included in the study. This is an older type of vaccine and is the only vaccine currently registered in the Netherlands. The effectiveness of the Nobilis vaccine against the current bird flu virus has not been tested before.
- HVT-H5 vaccine from Ceva Sante Animale
- HVT-H5 vaccine from Boehringer Ingelheim Animal Health
- DNA-vaccine from Huvepharma
"An important selection criterium for the candidate vaccines is the possibility to distinguish between animals that have been vaccinated and animals that produce antibodies due to a bird flu infection. With the three modern vaccines, this distinction can be made; they comply with the so-called DIVA principle," explains Nancy Beerens. The selected vaccines are already on the market in other countries, or at an advanced stage of development.
However, whether these vaccines are effective in preventing disease after infection with the current HPAI H5N1 virus found in Europe and can prevent the spread of the virus between laying hens was not tested before.
Studie design
Each vaccine was administered to ten laying hens. Subsequently, five chickens were infected with the bird flu virus. These were grouped together with the five chickens that were not infected. This study design investigated whether the virus would spread from infected chickens to uninfected chickens.
Both HVT-H5 vaccines have been found to be 100% effective in the trial
Results
Both HVT-H5 vaccines have been found to be 100% effective in preventing disease and mortality after infection with the HPAI H5N1 virus. This is in contrast to the other two vaccines in which disease was observed. The study showed that both HVT-H5 vaccines prevent virus spread between chickens. For these vaccines, the calculated reproduction rate (R-value) in the study was zero.
Further research
"Our study shows that both HVT-H5 vaccines are effective under laboratory conditions and prevent both disease and virus spread. These vaccines comply with the DIVA principle and are therefore good candidates for further research in practice," says Beerens. HVT-H5 vaccines can be administered in the egg or to day-old chicks in the hatchery.
The results of the conducted study cannot be extrapolated to the field. "It is important to investigate whether the vaccines work well under field conditions in poultry farms, how long the vaccines protect, and whether one vaccination is sufficient." The Dutch Ministry of LNV has commissioned a field study that will start this summer.
In addition, the vaccines still have to be registered in the Netherlands and the European Union. "There are still some hurdles to overcome, but the results of our research are an important first step towards vaccination against the bird flu virus in poultry," says Beerens.
Somewhat less reassuring is the fact that there are a number of H5 poultry vaccines in use around the world that have not been adequately tested against the current crop of H5N1 viruses.
A practice that may do more to hide the problem, than to solve it.
