Sokolov B P, Vladimirtseva E A, Zhdanov V M
Vopr Virusol. 1983 Mar-Apr(2):139-43.
Oligopeptide mapping showed the viruses H1N1 and H3N2 isolated from animals, unlike the majority of animal viruses with "animal" subtypes of the surface antigens, to have NP proteins typical of human H1N1 and H3N2 viruses which confirms their origin from human viruses.