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Table 1 Minimal evolutionary steps to acquire all 34 pandemic markers.

From: Conserved amino acid markers from past influenza pandemic strains

Initial strain

Region

Shift

Drift

H1N1 swine

Henan/Tianjin

H5, N1

199 PB2

117 NS1

H1N1 human

New Zealand

H9, N2

211 PB1

 

Australia

H7, N2

117 NS1

 

U.S.A., Asia

H5, N1

(one or both)

  1. First column shows the initial strain, the second column shows region where strain is found, the third column shows double reassortments taken (Shift) and column four shows the mutations (Drift) taken. The human case (row 2) involves three subtypes (H9N2, H7N2, and H5N1) and one or two mutations.