title: Antigenic shift and drift.
mesh_terms: D000595:Amino Acid Sequence; D005796:Genes; D006389:Hemagglutinins, Viral / Q000235:genetics*; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology*; D011995:Recombination, Genetic
chemical_list: D006389:Hemagglutinins, Viral