How to detect avian flu in vaccinated flocks?

What is the most effective strategy for highlighting the “silent circulation” of avian influenza within vaccinated flocks?

In October 2024, France launched its second campaign to vaccinate ducks against avian flu. However, this “considerably reduces mortality and clinical symptoms, classically used to detect the presence of the virus” underline the scientists.

Researchers from Inrae (1) and the National Veterinary School of Toulouse have studied several monitoring methods to quickly detect the presence of the pathogenic avian influenza virus (HPAI) in vaccinated duck farms. They therefore recommend concentrating surveillance efforts towards regular tests on dead ducks, in a press release shared by Inrae on January 6, 2025. Their study, which aims to optimize surveillance protocols, was published in the international journal Emerging Infectious Diseases (EID).

Up to 90% detection

Probability of virus detection and detection time were estimated by a mathematical model simulating the transmission of the virus in a flock of vaccinated ducks. The comparison focused on three early surveillance strategies:

• Event surveillance, which is based on an increase in mortality;
• Reinforced event surveillance, involving the carrying out of diagnostic tests on ducks found dead;
• Scheduled surveillance, based on carrying out diagnostic tests on a sample of live ducks.

“Weekly samples from dead ducks, or reinforced event monitoring, offer the best sensitivity and the earliest detection,” concludes the study. In fact, up to 90% of infected farms are detected during simulations.

Combine vaccination and surveillance measures

Sampling dead ducks therefore appears more effective than taking monthly samples from a sample of live ducks. They are preferred to limit the risk of silent traffic, according to the scientists behind the study. Conversely, “less effective and more costly programmed surveillance strategies” should be reduced.

Results which underline “the importance of a judicious combination between vaccination and surveillance measures, in order to preserve animal health and support the poultry sector in the face of current health challenges”.