The effectiveness of immunization can be evaluated through the results of immune monitoring. Immune monitoring generally employs serological methods and, when necessary, may also involve challenging immunized poultry with virulent strains under laboratory conditions. Commonly used serological methods include hemagglutination inhibition tests, agar gel immunodiffusion tests, neutralization tests, and ELISA. The number of samples collected from poultry should generally account for 2% of the total flock (pen or house), but must not be less than 30 samples.

The timing and frequency of monitoring can be determined based on practical circumstances. Generally, the first test is conducted 14 to 21 days post-vaccination, followed by subsequent tests every 1 to 3 months. There is currently no universally recognized standard for the required antibody titers in poultry after immunization. Poultry farms can establish minimum antibody requirements for several major infectious diseases based on available data and their specific conditions.

When evaluating antibody titers of tested samples, both the geometric mean titer and the proportion of samples falling below the minimum protective titer should be considered. Even if the average titer is relatively high, if a certain proportion of tested sera have titers below the critical protective level, booster immunization must be administered.

If challenge protection tests in the laboratory are used to monitor immunization effectiveness, these must be conducted in relevant external laboratories. The number of poultry tested must not be less than 10, and preferably should exceed 30. By challenging with a median lethal dose of virulent strain through the most sensitive route of inoculation and observing for 10 to 14 days post-challenge, the incidence and mortality rates can be recorded, providing a relatively accurate assessment of immunization effectiveness.