Vietnamese trials with a thermostable Newcastle disease vaccine (strain I2) in experimental and village chickens.

The Australian I2 strain of Newcastle disease virus was tested as a vaccine in the laboratory and in Vietnamese villages. The infectivity litre of lyophilised vaccine fell less than 1 log10 unit on storage for 6 days at 26-32 degrees C. Vaccine stored at similar temperatures induced high levels of immunity in laboratory chickens after storage for 17 days and in village chickens after storage for 21 days. I2 vaccine protected for at least 24 weeks after vaccination, and for 16 weeks after application in drinking water. Under laboratory conditions, I2 vaccine given by eye drop spread by contact to unvaccinated chickens, inducing in them both an antibody response and protective immunity. In villages, chickens vaccinated by eye drop, chickens receiving vaccine on food and chickens in contact with vaccinated chickens all resisted artificial challenge 6 weeks after vaccination. There were no adverse reactions to vaccination. Strain I2 was judged to be thermostable, avirulent and immunogenic, and suitable for use as a vaccine under village conditions.