Following a severe outbreak in 2010 and 2011, which resulted in the loss of 3.5 million animals, South Korea has mandated foot and mouth disease (FMD) vaccination on most livestock farms. This week, after FMD was confirmed in two cattle from two different farms in South Korea, investigators conclude that cattle on those farms likely were not vaccinated properly.

According to a report from the Korea JoongAng Daily, tests indicate 19% of the cattle on the farm with the initial case were producing antibodies for the FMD strains used in the vaccine. On the second farm with a positive FMD case, just 5% of the cattle tested positive for the antibodies.

Previous nationwide testing of vaccinated cattle showed 97.5% were positive for the antibodies, with 80% considered a benchmark for effective herd immunity. Producers in South Korea are required to vaccinate calves within two months of birth, with a booster vaccine two weeks later and subsequent vaccines every six to seven months.

Animal health officials concluded that the two affected farms did not vaccinate their cattle properly. Specifically, according to news reports, they failed to store their vaccines under proper refrigeration.

To ensure control of the outbreak, South Korea is requiring revaccination of the country’s 3.1 million head of cattle, at an estimated cost of $4.6 million.