The duration of immunity was studied for a 365-day period in swine vaccinated with a foot-and-mouth disease trivalent vaccine, inactivated for 48 hours with acetylethyleneimine and combined with an oil adjuvant. A satisfactory degree of immunity was afforded at 90 and 180 days postinoculation (DPI). At 365 DPI, vaccinated swine still maintained a degree of resistance to infection despite marked lowering of neutralizing antibody. At 6 months, lesions at inoculation sites were of very limited extent and appeared as scattered islands of small yellowish streaks of fibrous tissue and some spherical nodules. Histologically, lesions were multiple, foreign-body-type granulomas characterized by oil vacuoles, reticuloendothelial cell proliferation and fibrosis. Tissues surrounding lesions were normal. At 12 months, these lesions were almost impossible to locate. Microscopically, they were comparable to those observed at 6 months. Whether these lesions are more serious than those obtained with current products and other adjuvants and whether these constitute a carcass blemish remain to be determined. © 1969 Springer-Verlag.
