Genetic and antigenic characterization data generated at the Worldwide Influenza Centre for viruses with collection dates after 31 January 2023 until 31 August 2023 informed the WHO influenza vaccine composition meeting (VCM) in September 2023 when recommendations were made for the southern hemisphere (SH) 2024  influenza season. At the September 2023 VCM it was recommended to change the A(H1N1)pdm09 and A(H3N2)  vaccine components for the 2024 SH season. Previously, at the February 2023 VCM, which focused on data  from viruses collected after 31 August 2022 until 31 January 2023, it was also recommended to change the A(H1N1)pdm09 vaccine component for the 2023‑2024 northern hemisphere (NH) season.