translation.da: En eller flere af de tre pandemier i det 20. århundrede antages at være udgået fra et dyre- eller fugleinfluenzavirus, der ved mutation eller ved udveksling af gener med en human influenzastamme (såkaldt rekombination) er blevet i stand til at smitte mennesker og frem for alt at smitte fra menneske til menneske.
translation.en: At least some of the three pandemics during the last (20th) century are thought to have come from an animal or bird influenza virus that itself mutated or swapped genes with a human influenza strain (so called recombination) and acquired the ability to both infect humans and, more importantly, spread between them.