When Newcastle disease vaccine (La Sota strain) is used in drinking water for vaccination of specific pathogen free (SPF) baby and adult chickens, good protection was obtained even with a small dose of 100.000 EIR, (at least 95.9%).
Vaccination of matermally immune chicks of 10, 11 and 12 days old with this vaccine, did not give satisfactory results following the primary vaccination dose (protection of 50-55%). When a second ary vaccination dose was given to two groups of birds at two differ ent intervals following the first dose, i.e. after 14 and 24 days, the percentage of immune birds increased to 65 and 80% respectively.
The acquired immunity was quite satisfactory and reached 90%, when matemally immune chicks of 14 days old were primary vaccina ted with a dose of 2,500.000 EIDO HL titers in vaccinated birds could not be used as a criterion to judge on the protection percentage in challenged birds.