Capacity of attenuated swine fever vaccines to prevent virus carriers in the vaccinated pigs, after contact with field virus.

Virus carriers have been detected in pigs vaccinated with attenuated Swine Fever vaccines after challenge with field virus. Virus carriers were found only if the vaccination was made with 20 PD50 or less. Clinical protection was obtained already with 8 PD50. In insufficiently vaccinated pigs, virus was detected in the tonsils as long as 6 weeks after the virus challenge, by Immunofluorescence. A minimal potency of 100 PD50 is proposed as requirement for the acceptance of Swine Fever vaccines.