but as these vaccines are used
primarily in countries where ND is endemic this may not necessarily preclude their use. In the USA, the
9CFR 121.3b.818 states that NDV strains with ICPI values equal to or greater than 0.7 are virulent and
reportable, leaving NDV isolates of low virulence to be used as vaccines. The European Union stated in their
Commission Decision 93/152/EEC (European Commission, 1993) that for routine ND vaccination programs
the viruses used as live NDV vaccines are to be tested under specific conditions and have an ICPI of less
than 0.4 or 0.5, depending on the dose of vaccine given. The OIE Biological Standards Commission similarly
recommended in 2000 that in principle vaccines should have an ICPI