Identifying the viral and epidemiological factors behind the apparent global extinction of influenza B/Yamagata

Influenza B/Yamagata is linked to extinction after COVID-19–era contact reductions, with its lower basic reproduction number making it especially vulnerable in the early pandemic phase.

• Why it matters: The work addresses why one influenza B lineage disappeared while the other reemerged, separating epidemiological drivers from immunological or evolutionary explanations.
• What they did: The authors built a global model of influenza B lineages, imposed a transient contact reduction to mimic pandemic transmission changes, and fit parameters to reproduce pre-pandemic coexistence plus post-pandemic outcomes.
• The result: Model-based stochastic simulations indicate B/Yamagata extinction and suggest B/Victoria was also near extinction early on, enabling scenario testing for vaccination feasibility and potential reemergence in 2026–27.

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