On the phenomenon of weakening pathogenicity of H5N1

Several samples were tested this autumn and winter and H5N1 was found to be less pathogenic. Manifestations: sporadic death, egg production decline, mild respiratory symptoms, a small amount of yellow-green feces, autopsy lesions similar to H9. I wonder if any colleagues have encountered similar situations? Whether it is caused by vaccine universal prevention and chicken adaptability to the virus, please express your opinions.