Antigenicity of inactivated swine influenza virus concentrated by centrifugation

Swine influenza virus grown in fertile chicken eggs was inactivated with a 1:4000 dilution of formalin for three days. Centrifugation at 47,000 g for 1-3 hours concentrated the viral particles. Reconstitution to 1/10 the original volume for use as a vaccine resulted in a product having an HA titer of 1:64 to 1:512. Two doses of 4 ml given three weeks apart resulted in a serologic response in three of six gilts of breeding age. Experimental challenge of two vaccinated and two control gilts to swine influenze virus showed that vaccinated gilts did not react by production of a marked HI antibody response when compared to unvaccinated gilts.