ATAGI statement on the transition from quadrivalent to trivalent seasonal influenza vaccines in Australia

Overview of key points and updates 

• Australia is transitioning from using quadrivalent influenza vaccine (QIV) to trivalent influenza vaccine (TIV) formulations for influenza immunisation in our population. During the transition period, ATAGI supports the use of either QIV or TIV.
• In Australia, the TIV was used for many years until 2016, when the QIV became available on the National Immunisation Program (NIP). However, in late 2023, the World Health Organization (WHO) and the Australian Influenza Vaccine Committee (AIVC) recommended that the B/Yamagata lineage component is no longer warranted in seasonal influenza vaccines. This is because the Yamagata lineage of the influenza B virus has not circulated for several years.
• WHO recommends trivalent vaccines for use in the 2024–25 influenza season in the Northern Hemisphere and with select strains depending on whether using egg-, cell-, or recombinant-based technology. However, the B/Yamagata lineage component remains unchanged in any available QIV. 1
• The TIV includes the haemagglutinin antigen of an A/H1 subtype, an A/H3 subtype and a B lineage, which are selected to match the circulating strains for each influenza season as well as possible. The QIV comprises both B lineages of the influenza virus. 
• During the transition from QIV to TIV, Australia will ensure that the supply of vaccine is adequate and secure. Some TIV formulations may become available in 2025 to be used alongside QIV, which will continue to be available. It is anticipated that TIV may be used exclusively by the 2026 influenza season. 
• Studies comparing egg-based QIV with TIV have shown no significant differences in safety and reactogenicity outcomes. This indicates that a return to the TIV formulation for all influenza vaccines is not expected to adversely impact influenza vaccine safety.
• Studies have also demonstrated that, for each of the shared strains contained in the egg-based QIV compared with the corresponding TIV formulation, any differences in antibody response were minimal. This is true for both the standard-dose and the enhanced (high-dose and adjuvanted) influenza vaccines. Immunogenicity was consistent across age groups and in pregnant people.
• While there are no data comparing cell-based influenza vaccines, it is not anticipated that there will be any immunogenicity or safety differences between cell-based TIV and cell-based QIV.
• Annual vaccination remains the most important strategy to prevent influenza and its complications, and is recommended for all people aged ≥6 months. Even though the B/Yamagata lineage is no longer circulating, high disease burden associated with influenza A (H1N1 and H3N2) subtypes and the influenza B/Victoria lineage continues.