When trying to decrease the virus challenge to a piglet, it is first necessary to figure out where the virus is outside the pig, how it moves around the farm.
When asking the question, "How can influenza be controlled on a pig farm?" the first thing that comes to mind is "vaccines." The second thing is probably "gilts" and the third is "people." That order for answering the question is perfectly understandable given the evidence that shows that vaccines, particularly vaccines in sows, are commonly used on pig farms to protect piglets from influenza. Gilts and people are also important because both can be sources of new strains into farms, and gilts can be amplifiers of existing infections. All this translates into the need to have a comprehensive multi-prong approach to controlling influenza.
However, one side of the equation that is often forgotten is the need to decrease the viral challenge to susceptible populations such as newborn piglets. Piglets are born negative for influenza infections and piglets in endemically infected farms become infected rapidly prior to weaning. Unfortunately, even piglets born to vaccinated sows may become infected. Whether or not a piglet farrowed by a vaccinated sow becomes infected depends on how well the vaccine matches the influenza strains circulating in the herd. Both the quality and quantity of the immune response matters. When you understand that vaccination, that "No. 1 thing to control disease," is imperfect, it makes you realize how important it is to decrease the viral challenge by other methods.