Serum titers of swine immunized with chimeric virus BVP1. Groups of swine were immunized with 0.5 mg (▲), 5 mg (◆), 10 mg (■) of chimeric virus BVP1 or 5 mg of wild-type virus BaMV-S (○) or PBS (□). Swine sera were collected at the indicated time after immunization. Anti-VP1 titers were determined by ELISA. The animals inoculated with 0.5 mg BVP1 were boosted with the same amount of BVP1 four weeks after priming while those inoculated with 5 mg and 10 mg of BVP1 were boosted six weeks after priming.