Effectuality of Three Inactivated H5 Vaccines of Different Clades Against Newly Emerged Egyptian HPAI H5N1/2022 and H5N8/2019belonging to Clade 2.3.4.4b and Immunopathology of Both Viruses on Some Immune Organs

The H5Nx viruses belonging to clade 2.3.4.4b has become enormous intimidationglobally. Outbreaks resulting from this clade have been reported in various countriesresulting in an exceptional numeral bird mortalities. This work aimed to assess 3 H5vaccines of different clades (2.3.2 - 2.3.4 -2.3.4.4b) against newly emerged Egyptian clade2.3.4.4bHPAI H5N1/2022 and H5N8/2019 viruses in commercial. broiler chickens. Clade2.3.2 vaccine failed to protect clinically against both challenge viruses while, clade 2.3.4(Re-5) showed 87 % and 40% protection against H5N8 and H5N1, respectively. Clade2.3.4.4b showed 60% protection against H5N8 compared to 93% protection againstH5N1.Obtained results demonstrated that clade 2.3.4.4b H5N8 vaccine antigenicallymatched effectively with the newly emerged clade 2.3.4.4b H5N1 virus& could afford highlevel of clinical protection. Histopathological lesions were recorded in different collectedorgans including cerebrum, trachea, lung, spleen, thymus and bursa of Fabricius. Thelymphoid tissues displayed moderate to severe lesion scores including congestion, necrosisand depletion 0f lymphocytes. Thus, clade 2.3.4.4b viruses could have animmunosuppressive effect. Continuous evaluation of the validated AI H5 vaccines againstnewly emerging.AI strains is substaitional to deal with that intimidating remark. Also, thevaccinal seed strains should updated regularly in order to obtain utmost protection levelsand assure presence of antigenic matching among prevailing strain and vaccinal strains.