IFNG and infection: Without at this point specifying exact NA titers or IFN-γ+ T-cell numbers, surveying the literature, we can postulate that serum NA titers in adult pigs at vaccination or even upon challenge generally remain relatively low (≤1:16) [76,80,118,119,165,167,169]; conversely, in young pigs the vaccination NA titers are often undetectable or low (≤1:8) but upon challenge or infection, NA titers can be much higher than the adult pig range and reach the assay maximum (1:512) [50,83,108,117,120,130,142,171].