WUR study shows: vaccination reduces the risk of avian influenza outbreaks
- KM (Kim) Bouwman-te Selle, PhD
- WR Onderzoeker
Vaccination of laying hens against highly pathogenic avian influenza (HPAI) reduces virus transmission, mortality and outbreak risks in the poultry sector. This was shown in a multi-year field study by Wageningen University & Research, conducted with Royal GD and Utrecht University, investigating two HVT-based H5 vaccines under Dutch commercial farming conditions.
At the start of the research project on the effectiveness of two commercial vaccines against highly pathogenic avian influenza (H5N1), flocks received one of two vaccines: VAXXITEK HVT+IBD+H5 or Vectormune® AI. The vaccinated laying hens were monitored for more than 85 weeks in order to assess the effectiveness of vaccination throughout the entire production cycle. The study was commissioned by the Dutch Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN) and funded by the ministry together with the Dutch poultry sector, represented by AVINED.
Reduced virus transmission and smaller outbreaks
Transmission experiments were conducted to investigate how effective vaccination is in limiting the spread of the avian influenza virus within flocks. At different ages, groups of hens were brought to the facilities of Wageningen Bioveterinary Research (WBVR), where half of the birds were exposed to the H5N1 avian influenza virus.
The study showed that one unvaccinated adult laying hen can infect on average more than six other hens. In vaccinated hens, virus transmission (virus spread) occurred significantly slower. The extent of reduced virus transmission was strongly associated with the antibody levels within the flock: groups with high antibody levels showed clearly lower transmission rates than groups in which more birds had lower antibody levels.
Based on the collected field and transmission data, the researchers performed flock-level modelling. “The results show that vaccination substantially reduces the likelihood of an outbreak,” says WBVR researcher Kim Bouwman, project leader of the study. Without vaccination, the probability of an outbreak following virus introduction is approximately 96% percent. “This percentage decreases to 10 to 30% in vaccinated flocks, depending on the vaccination strategy and the use of a booster vaccination.” The scale of outbreaks was also found to decrease considerably.
Importance of high and stable antibody levels
To monitor the immune response of the laying hens, birds on the poultry farms were sampled monthly throughout the study. Average antibody levels increased during the rearing period and remained high throughout the production phase. Fluctuations were observed, particularly in flocks that received only a primary vaccination. Flocks that also received a booster maintained consistently high antibody levels throughout the entire production cycle. “These results demonstrate that it is important to vaccinate, but to achieve and maintain sufficiently high and uniform antibody levels within a flock,” Bouwman explains.
Vaccination proven safe
The vaccination was shown to be safe for the hens. No visible side effects were observed, flock health remained stable, and mortality stayed within normal levels for commercial production systems. Egg production also reached normal levels. No negative effects of vaccination on production performance or animal welfare were identified.
Monitoring remains essential
Because vaccination reduces clinical signs and mortality, outbreaks may become less visible. The researchers therefore stress that vaccination must always be combined with active monitoring. Without monitoring, only a limited proportion of outbreaks would be detected on vaccinated farms. With an appropriate surveillance system, more than 93 per cent of outbreaks can be detected in time.
In addition, more than 8,600 blood tests showed that field infections in vaccinated flocks remain readily detectable using current diagnostic tests. Of the samples analysed, 99.8 per cent tested negative, indicating the absence of virus circulation. This was confirmed by negative PCR results from samples taken from deceased hens.
Food safety
The safety of poultry products was also investigated. Only occasional PCR-positive samples were detected on eggshells or in tissues, without infectious virus being isolated. According to the researchers, the results indicate a minimal risk to food safety.
Towards sustainable control of avian influenza
The researchers conclude that vaccination is an effective additional strategy for controlling avian influenza in poultry. Although vaccination does not completely prevent virus transmission within a flock, it significantly reduces virus spread, mortality and the risk of large-scale outbreaks. Combined with targeted monitoring and existing biosecurity measures, vaccination therefore offers prospects for more sustainable control of avian influenza, benefiting animal health, public health and the poultry sector.
Read the full research reports:
Vaccination of poultry with HVT-based H5 vaccine against highly pathogenic avian influenza (HPAI) H5N1 virus (clade 2.3.4.4b)
FAQ: Vaccination against avian influenza in laying hens
Avian influenza (bird flu) can cause major outbreaks in poultry, leading to high mortality, animal welfare concerns and significant economic losses. When the outbreaks in 2021 started it became clear there was no registered vaccine in the EU against H5N1, the virus that still circulating across the world and infecting wild birds as well as commercial poultry farms.
To study whether vaccination can help to protect poultry, by reducing the spread of the virus, lowering mortality and limits the impact and number of outbreaks in commercial poultry farms, the efficacy of two commercially developed vaccines was evaluated.
Chickens were vaccinated at day of hatch, monitored throughout their entire production cycle on two commercial farms in the Netherlands. At different points in time during the production cycle, subsets of chickens were infected in contained facilities to determine the protection offered by the vaccines against a challenge with the circulating virus.
Yes. The results show that vaccination is safe and well tolerated by laying hens. No vaccine-related health issues were observed, and mortality levels remained within normal ranges for commercial poultry farms.
No negative effects on egg production were found. Vaccinated flocks reached normal production levels and peak egg production.
No, vaccination does not fully stop transmission within a flock. However, it significantly reduces virus spread, virus shedding and mortality. This means outbreaks are less severe and easier to control.
Model calculations based on the results obtained in this study regarding how fast the virus spreads in a flock, predict that vaccination can reduce the probability of an outbreak after virus introduction from around 96 percent to approximately 10 - 30 percent. It also reduces the expected outbreak size from about 14 farms to just 1 or 2 farms.
Yes. The surveillance systems remain effective. More than 99.8 percent of samples tested negative in DIVA monitoring, and there was no evidence that vaccination masks infections when proper testing is applied.
The timeline for introduction of a vaccine against bird flu is not clear yet. Based on the results of this study and the outcome of other European studies, the Dutch Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN) will take action towards implementation of this addition to the regular poultry vaccination programme. For more information, please refer to the Ministry of LVVN.
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