Vaccination of Chicks with Live Attenuated Subtype B Avian Metapneumovirus Vaccines: Protection Against Challenge and Immune Responses Can Be Unrelated to Vaccine Dose

Live attenuated subtype B avian metapneumovirus (aMPV) vaccines from two different commercial sources (Vac 1 and Vac 2) were used to vaccinate two groups of day-old specific-pathogen-free chicks. The chicks were challenged at 21 or 49 days of age with a virulent subtype B virus. Parameters compared were persistence of vaccine viruses, their ability to induce humoral antibody responses, and the protection they offered against virulent challenge....