Low passage vaccine: A low passage vaccine contains virus particles which have been attenuated, or weakened, less than those in the "average" vaccine.
(A low passage vaccine; contains; virus particles which have been attenuated) (virus particles; have been attenuated; ) (A low passage vaccine; weakened less; )
A low passage vaccine virus particles A low passage vaccine
contains have been attenuated weakened less
virus particles which have been attenuated