We report classical swine fever outbreaks occurring in naive pig herds on Jeju Island, South Korea, after the introduction of the LOM vaccine strain. Two isolates from sick pigs had >99% identity with the vaccine stain. LOM strain does not appear safe; its use in the vaccine should be reconsidered.
Keywords: Jeju Island; LOM strain; South Korea; classical swine fever; classical swine fever virus; livestock; modified live vaccine; outbreak; pigs; residual virulence; vaccination; viruses.