optimizing the process of inactivating influenza virus subtype h9n2 by formalin in the production of killed avian influenza vaccine

Avian influenza is one of the most important diseases in avian industry, which also threats human population. thus, vaccination is necessary for controlling this viral disease. in this study, killed vaccine of avian influenza subtype h9n2 and formalin solution (for virus inactivation) were used. it is necessary to study the effect of different factors such as formalin concentration, as well as incubation temperature and duration on inactivation process. for this purpose, after preparation and measurement of antibody titers of vaccinal strains of avian influenza, 27 experimental samples of h9n2 avian influenza virus were prepared at different formalin concentrations (0.1%, 0.05%, and 0.025%), at different incubation temperatures (4 °c, 25 °c, and 37 °c), and in different incubation durations (12, 18, and 24 h). in addition, three control samples were prepared at three different test temperatures without adding formalin. all the samples were evaluated by inactivation test, hemagglutination assay, and measurement of free formaldehyde. all the experiments were repeated within three consecutive periods. considering the findings and destructive effects of long incubation durations at 37°c on antigens, the temperature of 25 °c was more suitable. furthermore, the free formaldehyde amounts at different concentrations at 25 °c were slightly different in comparison with 37 °c. therefore, formalin concentration of 0.1% at 25 °c completely inactivated the virus within 24 h and was proposed as the optimal condition.