Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus , the presence of non-reactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses . Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus , the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses .