Uncleaved HA from influenza A/Victoria/2570/2019, the egg-derived A(H1N1)pdm09 component of the 2021 vaccine (PDB 9GSP). HA1 is colored by the classical antigenic region each residue belongs to, taken from Table 2 of Wilson et al. (2015), Virology 485:252-62, which carries the regions Caton and colleagues mapped on A/PR/8/34 into the numbering of the 2009 pandemic lineage:
Every residue carries its site in HA1 or HA2 numbering — 192_HA1, 14_HA2 — shown on
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This is an HA0: the protease site that would cut HA1 from HA2 is uncut, and the loop carrying it — HA1 324-327 and HA2 1-6 — is disordered, so it is missing from every view here rather than hidden by it.
Uncleaved HA from influenza A/Victoria/2570/2019, the egg-derived A(H1N1)pdm09 component of the 2021 vaccine (PDB 9GSP). HA1 is colored by the classical antigenic region each residue belongs to, taken from Table 2 of Wilson et al. (2015), Virology 485:252-62, which carries the regions Caton and colleagues mapped on A/PR/8/34 into the numbering of the 2009 pandemic lineage:
Glycans are hidden.
Every residue carries its site in HA1 or HA2 numbering — 192_HA1, 14_HA2 — shown on
mouseover.
This is an HA0: the protease site that would cut HA1 from HA2 is uncut, and the loop carrying it — HA1 324-327 and HA2 1-6 — is disordered, so it is missing from every view here rather than hidden by it.
Structure of H1N1 HA (PDB 9GSP) with red indicating every site that differs between A/California/07/2009 (the 2009 pandemic vaccine strain) and the subclade D.3.1 strain A/Missouri/11/2025 (the H1N1pdm09 component of the 2026-2027 vaccine). Sites that did not change shown in gray.
12 of the 38 ectodomain mutations are at sites in the classically defined antigenic regions: five in site Sa, three in site Sb, one in site Ca1, two in site Ca2, one in site Cb. All 12 are among the 37 at sites in the structure shown here.
The HA sequences for the two strains are FJ966974 and PV886191.
Structure of H1N1 HA (PDB 9GSP) with red indicating every site that differs between subclade D.3.1 (A/Missouri/11/2025, the H1N1pdm09 component of the 2026-2027 vaccine) and subclade D.3.1.1 (A/Andalucia/PMC-00977/2025, collected in 2025). Sites that did not change shown in gray.
They differ at 4 sites:
The HA sequences for the two strains are PV886191 and PX399795.
Structure of H1N1 HA (PDB 9GSP) with red indicating every site that differs between subclade D.3.1 (A/Missouri/11/2025) and subclade D.3.1.1 (A/Andalucia/PMC-00977/2025), and indigo showing site 155, where G155E arises on the D.3.1.1 background, the same indigo that antigenic region Sa is given in the first two views.