 Low anti-SeV antibodies background does not block the ability of SeV-base vaccine to promote antigen-specific T cell immunity.Wild type, attenuated SeV has been used in clinical trials involving both adults and children to immunize against HPIV-1.The virus administration in the form of nasal drops in doses ranging from 5 × 105 50% embryo infectious dose (EID50) to 5 × 107 induced the production of neutralizing antibodies to the human virus without any measurable side effects.The results of these trials represent an evidence of safety for humans of replication competent Sendai virus administration.SeV antibodies that cross-reactive with HPIV-1 antibodies are present in most people, however, majority of people do not have high titer of these antibodies.