Selection Map of influenza A HA (H3 serotype). Positively selected variants are at those codons where one or more mutations from the consensus confer selective advantage on the virus (capitalized and listed below the consensus). Lowercase letters indicate mutations where the neutral drift hypothesis is not ruled out. Negatively selected variants are not shown. The antigenic sites  are colored: A, red; B, yellow; C, green; D, blue. The selective advantage of the mutations at sites 156, 186, and 276 may have been conferred during viral passage in culture, so these mutations may not be positively selected in the field [58, 59].