Never before have chickens in the Netherlands been vaccinated against avian flu in a field trial, but that is no longer the case as 1,800 day-old chicks recently received a vaccination against highly pathogenic avian influenza (HPAI) H5N1. This marks the start of a field trial, which is taking place on behalf of the Ministry of Agriculture, Nature and Food Quality (LNV). It is an important step toward large-scale vaccination of poultry against the virus.

"Avian flu is a serious disease that has affected the poultry sector enormously, it affects both the animals and the farmers, and of course many wild birds have also died because of it. We are therefore taking action together to reduce the number of infections in poultry,” said Piet Adema, Minister of LNV.

Field trial vaccine

Previous research in the laboratory at Wageningen Bioveterinary Research (WBVR) has shown that two vector vaccines against HPAI are effective against spreading the virus. The ministry is now having Wageningen University & Research (WUR), Royal GD (Animal Health Service) and Faculty of Veterinary Medicine at Utrecht University investigate whether these two vaccines are also effective at poultry farms.

At the start of the field trial, chicks were divided into several test groups. At regular intervals, a number of chickens from the field trial will be tested in the laboratory, under controlled conditions, to investigate the effectiveness against infection. During the trial the chickens are intensively monitored and controlled, in line with the new European regulation. This field trial is a scientific study, and the products of the vaccinated chickens will not be marketed. Chickens are already being vaccinated against various diseases.

The trial on the two farms will last until the third quarter of 2025. First results are expected in the second quarter of 2024. Under field conditions, the effectiveness of a vaccine may differ from controlled conditions in a laboratory. For example, at a poultry farm, the housing and barn climate are different, the animals are vaccinated against more diseases, and there are other germs present in that could influence the effectiveness of a vaccine. It is important that the vaccines not only provide protection against disease symptoms, but mainly prevent the spread of the virus.

Avian flu poultry vaccination approach

The Dutch government wants to enable vaccination responsibly, with animal and public health and animal welfare in mind. Therefore, a step-by-step approach was chosen. In addition to the field trial, a pilot will be conducted to vaccinate a larger number of poultry farms in the Netherlands. The pilot is expected to take place on several poultry farms in the second quarter of 2024. The condition is that the vaccine has European approval by then and that the results of the first laboratory test are known.

The pilot will also pay close attention to the effects of vaccination on poultry trade and the establishment of a surveillance program. That surveillance program is to detect any infection on a vaccinated farm, something that might happen despite vaccination, as soon as possible. This will minimize the chance that the virus will still continue to circulate.

Even as progress is made on the vaccine front, it is still very important that poultry farmers stay alert, practice good biosecurity, and report a suspicion of avian flu. This is currently still the best way to minimize the risk of infection.