Mo. Rev. Stat. § 267.554
Notwithstanding the other provisions of sections 267.551 to 267.556, the director shall be empowered to require the use of another type of vaccine developed after January 1, 1984, found to be more effective than the vaccine, brucella abortus.
(L. 1983 1st Ex. Sess H.B. 24 § 4)
Effective 1-1-84