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public health · virology

Influenza seasonal strains

This illustrative chronogram separates selected H1N1 and H3N2 influenza A strains by season. The coloured clades make the two subtypes easy to distinguish, while the years-before-2025 scale makes the temporal framing explicit. It is a compact example of how a time-calibrated tree can organize a small selection of strains.

Type Phylogenetic treeStandard Newick + NHX extensionsEngine schematex-phyloUpdated 9/24/2026
Influenza A Seasonal Strains
Drawing preview
The request

“Create an illustrative 2025 influenza A chronogram with H1N1 strains from 2021 and 2022, H3N2 strains from 2021, 2022 and 2023, highlighted H1N1 and H3N2 clades, and a years-before-2025 scale.”

Then tryAdd an H3N2 2024 strain.Change the reference year to 2026.
What is in this drawing

Read the decisions behind it.

01Season labels

Include the strain subtype and season.

02Clades

Highlight H1N1 and H3N2 separately.

03Time scale

State the reference year on the chronogram.

Use this as an illustrative communication aid; surveillance conclusions need source data and analysis.

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FAQ

Common questions

What does the seasonal label show?

It identifies the subtype and year used for each selected strain.

Why use a chronogram?

A chronogram makes the time framing of a strain comparison explicit.

Is this surveillance evidence?

No. It is an illustrative example and does not replace a sourced surveillance analysis.