The present study aimed to detect the incidence of protozoan parasites and their disease severity in balady chickens in relation to the routine viral vaccinations against Newcastle, Infectious bronchitis and Infectious bursal diseases. For this purpose, eight hundred balady chicks divided to 8 equal groups, 4 groups not artificially infected by Eimeria while the other 4groups were artificially infected. The
collected samples were examined daily and the detected protozoa were Eimeria spp. (31%) and Cryptosporidium spp. (10%) during the vaccination period. The vaccinal dynamic revealed that the highest incidence of Eimeria (64%) was recorded in G2, while minimum oocyst count / gm feces (0.25×103 ) in G 6 at 14 days old, then a rapid, increase, specially 1- 2 days old after each vaccination to reach maximum (35×103) at the 30 days old. The lowest incidence of Eimeria spp., was in G 1& G3 (0%) and the minimum oocyst count /gm feces (0.1×103) and gradually increased to reach maximum (0.45×103
) at 18 days old, then decreased again to (0.1×103) at the end of experiment in G7.
It was concluded that stress caused by viral vaccinations affecting both incidence and severity of protozoal diseases, especially Eimeria on non-treated chicken groups.