Therefore, if a pig becomes infected by both types of viruses ​ — one sort that infects animals and another sort common to humans — ​ the genes of the two strains can get mixed together. The result can be a totally new strain of influenza, one to which humans have no immunity.
Tāpēc, ja cūka ir inficēta ar abiem vīrusu veidiem — gan to, kas izraisa saslimšanu dzīvniekiem, gan to, kas raksturīgs cilvēkiem, — abu veidu vīrusu gēni var krustoties, veidojot pilnīgi jaunu gripas paveidu, pret kuru cilvēkiem nav imunitātes.