Health Report - Separate stories podcast Changes to flu vaccines
Apr 3, 2026
Professor Patrick Reading, director of the WHO Collaborating Centre at the Doherty Institute and influenza expert. He explains original antigenic sin and how past immune memory shapes vaccine responses. He outlines 2026 vaccine strain changes and which variants have dominated recent seasons. He also compares injectable, enhanced elderly, and nasal live attenuated vaccine options.
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Original Antigenic Sin Shows Long H1N1 Cross Reactivity
- Original antigenic sin means immune memory from early exposures can override responses to new vaccine strains and shape later immunity.
- Doherty Institute study found 1994 vaccine-induced antibodies cross-reacted with H1N1 and B strains up to 30 years later, but not H3N2.
H3N2 Evolves Faster Than Other Seasonal Strains
- H3N2 evolves faster than H1N1 and B, requiring more frequent vaccine updates and causing most vaccine-match problems.
- Patrick Reading calls H3N2 the "problem child" because of its rapid antigenic and genetic change.
2026 Vaccine Updated H1N1 And H3N2 For Better Match
- The 2026 Southern Hemisphere vaccine updated H1N1 and H3N2 components while keeping the B component the same.
- The updated H3N2 better matches the circulating K variant that caused a late 2025 extended season in Australia.