Aerosol vaccination against Newcastle disease using the Ulster strain

The Ulster strain of Newcastle disease when administered as an aerosol vaccine has been shown to give a level of protection which is slightly lower than that produced by a commercial Hitchner B1 strain but which is not associated with any respiratory reaction. Both strains proved to be poor vaccines when used in chickens with high levels of maternal antibody. When used for vaccination of susceptible chickens the Ulster strain produced protection to experimental challenge for up to 3 weeks. Revaccination of these chickens with B1 vaccine produced a secondary response which was significantly higher than in the groups vaccinated initially with B1 vaccine. It is suggested that primary vaccination of fully susceptible chickens with the Ulster strain will induce a high degree of immunity with less reaction in the respiratory tract than is found to occur with currently used vaccines. This initial vaccination may then pave the way for further immunisation with higher levels of protection and less damage to the respiratory system.