Vaccination of chicken embryos with escape mutants of La Sota Newcastle disease virus induces a protective immune response., Mast, Jan, Nanbru Cécile, Decaesstecker Mireille, Lambrecht Bénédicte, Couvreur Bernard, Meulemans Guy, and van den Berg Thierry , Vaccine, 2006 Mar 10, Volume 24, Issue 11, p.1756-65, (2006)