H1_prot_struct

Subclade D.3.1.1 mutations (relative to the 2026 and 2026-2027 vaccine) also indicating sites 155 and 157

Structure of H1N1 HA (PDB 9GSP) with red indicating every site that differs between the 2026 and 2026-2027 vaccine strain (A/Missouri/11/2025, subclade D.3.1) and subclade D.3.1.1 (A/Andalucia/PMC-00977/2025), and indigo indicating sites 155 and 157 of antigenic region Sa.

Subclade D.3.1.1 and D.3.1 differ at 4 sites (shown in red):

One mutation in antigenic region Ca2: A139D
Three additional HA1 mutations outside the defined antigenic regions: R113K, E283K, K302E

Sites 155 and 157 are colored indigo, since G155E and S157L have a substantial antigenic effect in D.3.1.1.

Subclade D.3.1.1 mutations (relative to the 2026 and 2026-2027 vaccine)

Subclade D.3.1.1 and D.3.1 differ at 4 sites:

One mutation in antigenic region Ca2: A139D
Three additional HA1 mutations outside the defined antigenic regions: R113K, E283K, K302E

Classically defined antigenic regions of influenza H1 HA

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 site 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:

indigo — site Sa, 13 sites: 124, 125, 153-157, 159-164
cyan — site Sb, 12 sites: 184-195
green — site Ca1, 11 sites: 166-170, 203-205, 235-237
purple — site Ca2, 8 sites: 137-142, 221, 222
teal — site Cb, 6 sites: 70-75
light gray — HA1, not in a defined antigenic region
mid gray — HA2

Sites are numbered in HA1 numbering, and all 50 of them are modeled in 9GSP. The regions are disjoint, so every colored site belongs to exactly one of them.

Every residue carries its site in HA1 or HA2 numbering — 192_HA1, 14_HA2 — shown on mouseover.

Glycans are hidden.