The main methods of influenza prevention in swine populations are vaccination and biosecurity. Since swine influenza is a viral, not bacterial disease, antibiotics are not effective, except when used to treat secondary bacterial infections that coexist with influenza.
Several different swine influenza virus (SIV) vaccines are on the market. Most of these products contain swine H1N1 and H3N2 subtypes. Others also include an H1N2 subtype. Many of these SIV vaccines are combination vaccines that also include antigens against other pathogens such as Mycoplasma hyopneumoniae or erysipelas. Some, designed for use in sows and gilts, are combined with antigens against reproductive problems like leptospirosis and parvovirus. In addition, there is currently one vaccine that is directed against the pandemic H1N1 subtype on the market. Less often used, but available to veterinarians, are autogenous vaccines, which are manufactured from SIV strains that are isolated from the particular farm using the vaccine.
Current swine influenza vaccines are killed virus vaccines. As such, most of these vaccines require two doses given 2 – 4 weeks apart.
In practice, most SIV vaccines are used in sows. Sows that properly respond to the vaccine will produce a high level of antibody and pass this along to their piglets. In general, this maternal antibody will often persist long enough to protect an individual pig through the nursery phase. When clinical influenza is a problem in finisher pigs, then vaccination of nursery/finisher pigs may be considered. However, pigs that have high levels of maternal antibodies from vaccinated sows may not respond well to vaccine if they have a high level of SIV antibodies in their bloodstream at the time of vaccination.
The effectiveness of swine influenza vaccines depends on many things, not least of which is the particular strain or subtype of virus included in the vaccine, and how similar it is to the viruses encountered in the field. Research is ongoing to develop vaccines that can better cross-protect against many different strains of SIV.
Biosecurity is a critical means of protecting groups of pigs from infection with SIV, although many swine operations report outbreaks in the face of good biosecurity procedures. Isolation of incoming animals, all-in all-out production, and management of people and animal traffic are important in order to avoid infections with novel strains of influenza that might otherwise have been avoided.