PLS: Vaccination of poultry against highly pathogenic avian influenza – Part 2. Surveillance and mitigation measures

Published date:

Background to the scientific opinion

  • The European Union (EU) has experienced an epidemic of highly pathogenic avian influenza (HPAI) in wild and domestic birds in recent years. 
  • Vaccination can be considered in addition to already implemented measures (e.g. surveillance, biosecurity and early detection) to prevent and control the spread of HPAI.
  • According to EU legislation, after vaccination, enhanced surveillance of vaccinated poultry is required to detect early any potential outbreaks of the HPAI virus and to demonstrate that HPAI is not present in vaccinated areas. 

What was EFSA asked to do?

  • The European Commission asked EFSA to provide an overview of available HPAI vaccines, their efficacy against circulating viruses and an assessment of various vaccination schemes to inform decisions on possible vaccination strategies. These topics were addressed in EFSA’s first scientific opinion on HPAI vaccination.
  • EFSA was also asked to assess surveillance strategies for early detection of HPAI virus and demonstrate freedom from HPAI during emergency and preventive vaccination, as well as restrictions and risk-mitigation measures, in vaccinated farms and areas. This is covered by this second scientific opinion.

How did EFSA carry out this work?

  • EFSA issued its first scientific opinion on HPAI vaccination in October 2023: https://doi.org/10.2903/j.efsa.2023.8271
  • In the second scientific opinion, information on surveillance strategies was collected from the legal framework of the Delegated Regulation (EU) No 2023/361 and alternatives for each vaccination scenario (emergency and preventive) were considered. The World Organisation for Animal Health (WOAH) recommendations were also taken into account. Key attributes and performance indicators were defined according to the objective of the surveillance.
  • The different diagnostic tests that can be used as part of HPAI virus surveillance were described and a qualitative assessment was given to provide an indication of the appropriate diagnostic methods tailored to the surveillance objectives and sample type.
  • EFSA used serological data from experiments conducted on ducks, turkeys, and chickens by the national reference laboratories for avian influenza (AI-NRLs). These data were analysed to guide Member States in monitoring vaccine-induced immunity and distinguish between vaccinated birds and those infected with HPAI, based on their immune response. 
  • The effectiveness of surveillance strategies was assessed using mathematical modelling. 
  • The data used were derived from four sources:
    • EFSA’s first scientific opinion;
    • primary introductions of HPAI in poultry in the Netherlands; 
    • serology from experimental trials in Belgium, France, Italy, and the Netherlands; 
    • poultry mortality in France and the Netherlands.

What were the limitations/uncertainties?

  • Field studies are scarce on the effectiveness of different surveillance schemes to be applied after vaccination for the early detection of the HPAI virus and to demonstrate freedom from disease. 
  • Uncertainties exist in the assessments of surveillance strategies at farm and area levels due to the use of values (real or assumed) retrieved from previously published studies that may not be representative of all scenarios and poultry production systems in Europe.

What were the outcomes and their implications?

Outcomes

  • Clear insights were given into the effectiveness of different surveillance strategies for the two vaccination scenarios (emergency and preventive) by poultry species (chicken layer, turkey, and duck), specifying the number of birds to be tested, the diagnostic method to be selected and the sampling interval.
  • An evaluation of restriction and mitigation measures as well as proposals for alternative testing strategies were provided to enable safe movements of vaccinated birds. 
  • Recommendations were given for future scientific studies to address knowledge gaps.

Implications

  • EFSA’s scientific advice on HPAI surveillance strategies and risk mitigation measures will inform EU Member State policymakers and risk managers about potential surveillance strategies to be implemented in vaccinated areas for the early detection of HPAI outbreaks and to demonstrate freedom from disease.
  • The assessment of restrictions and risk mitigation measures will enable the safe movement of vaccinated poultry.

What are the key recommendations?

Different combinations of testing type, sample type, sample size, and sampling interval across different poultry species created a range of effective active surveillance options for the early detection of HPAI outbreaks during emergency vaccination as well as for demonstrating freedom from disease following preventive vaccination. The surveillance strategy should be selected according to the country's specific circumstances and resources. 

In relation to active surveillance for the early detection of HPAI outbreaks in vaccinated farms during emergency vaccination:

  • for chicken layers, ducks, and turkeys, effective options based on molecular testing of dead birds at a certain sampling interval were identified;
  • for ducks only, molecular and serological testing of live birds proved to be an effective surveillance strategy.

For active surveillance to demonstrate freedom from disease in vaccinated areas following preventive vaccination: 

  • for chicken layers, ducks, and turkeys, effective options based on molecular testing of dead birds with variations in sampling intervals and proportions of vaccinated flocks (100%, 50% and 25%) were identified.

Passive surveillance in unvaccinated farms in vaccinated areas is always recommended to enhance the overall sensitivity of the surveillance. During vaccination, passive surveillance is also applied to vaccinated flocks if, for example, an unusual increased mortality is observed between two consecutive sampling events.

Glossary

Active surveillance: efforts to detect disease through activities initiated under a defined protocol.

Chicken layers: female chickens raised and maintained for the purpose of laying eggs.

Emergency vaccination: vaccination of poultry in areas around an HPAI outbreak.

Passive surveillance: reporting to the health authorities of suspect cases raised by increased mortality, other signs of serious disease or significantly reduced production rates.  

Preventive vaccination: vaccination of poultry in areas in which there is no current HPAI infection.

Disclaimer

  • This plain language summary (PLS) is a simplified communication of EFSA’s Vaccination of poultry against highly pathogenic avian influenza – Part 2. Surveillance and mitigation measures. The full EFSA opinion can be found here.
  • The purpose of the PLS is to enhance transparency and inform interested parties on EFSA’s work on the topic using simplified language to present a summary of the main findings.

Reference

Vaccination of poultry against highly pathogenic avian influenza – 2. Surveillance and mitigation measures. DOI: https://doi.org/10.2903/j.efsa.2024.8755