Which influenza virus types predominated in the 2022‑2023 season compared to the 2023‑2024 season?

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Last updated: November 9, 2026 • View editorial policy

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Influenza Virus Types: 2022-2023 vs 2023-2024 Seasons

The 2022-2023 season was characterized by early Influenza B/Victoria dominance followed by late-season Influenza A(H1N1)pdm09, while the 2023-2024 season was predominantly Influenza A(H3N2) throughout. 1

2022-2023 Season Pattern

The 2022-2023 influenza season showed a biphasic viral distribution:

  • Early season (fall/early winter): Influenza B/Victoria lineage predominated
  • Late season (late winter/spring): Influenza A(H1N1)pdm09 became dominant
  • Overall severity was moderate with 199 pediatric deaths 1
  • Hospitalization rates: 92.3/100,000 in children 0-4 years and 23.5/100,000 in children 5-17 years 1

This unusual pattern was notable because influenza B typically circulates later in the season, but in 2022-2023 it appeared first, followed by the H1N1 surge.

2023-2024 Season Pattern

The 2023-2024 season demonstrated a more typical single-virus dominance:

  • Influenza A(H3N2) predominated throughout the entire season 1
  • Overall severity remained moderate with 184 pediatric deaths 1
  • Hospitalization rates were comparable to the prior season: 86/100,000 in children 0-4 years and 34.5/100,000 in children 5-17 years 1
  • Peak activity occurred in late December 2023 (15.49% of outpatient visits in children 0-4 years) 1

Key Clinical Implications

The shift from dual-wave B/Victoria and A(H1N1)pdm09 circulation to H3N2 dominance has important implications:

  • Vaccine effectiveness varied significantly: The 2022-2023 vaccine showed 49% effectiveness against B/Victoria and 29% against A(H1N1)pdm09 overall, while 2023-2024 data showed variable effectiveness against H3N2 1
  • Age distribution remained consistent: Children <1 year had the highest hospitalization rates in both seasons (128.3/100,000 in 2023-2024) 1
  • Underlying conditions: Approximately 65-70% of hospitalized children had ≥1 underlying condition in both seasons, with asthma being most common (22.9% in 2022-2023, rising to 28.1% in 2021-2022) 1

Important Context

Influenza B/Yamagata has not circulated since 2020, leading to the removal of this component from seasonal vaccines starting in 2024-2025 2. This represents a fundamental shift in influenza ecology post-COVID-19 pandemic. The 2022-2023 season's B/Victoria circulation may have represented a transitional epidemiological pattern as influenza re-established typical circulation patterns after pandemic disruptions 1.

Vaccination coverage declined in both seasons: 62.3% in 2022-2023 dropping to 53.9% by May 2024, with particularly low coverage among non-Hispanic Black children (49.1%) and rural populations (39.9%) 2. This declining coverage occurred despite moderate-to-high disease burden in both seasons, with over 50% of pediatric deaths occurring in unvaccinated children who were vaccine-eligible 1.

References

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