Defining swine influenza virus

While genetic analyses of influenza viruses have told us a great deal about the epidemiology and origin of SIVs in our swine population, they do not provide us with information as to whether SIVs with different genetic sequences will react the same way in the pig or whether disease will be prevented by administering the usual vaccine. Studies in Europe^20,24 and in the United States²⁵ have shown that even when antigenic (ie, serologic) and genetic differences exist among several circulating SIVs, vaccination with a single type of SIV vaccine may protect against the SIV variants if the pigs have sufficiently high concentrations of serum antibodies. It is important now, more than ever, to conduct cross-protection and challenge studies with the variant SIVs that are found in swine worldwide and to determine whether current vaccines will continue to be effective in our US swine population.