Seasonal Flu Shots Give Long-Term Immunity Against Future Strains
08 Apr 2026
Researchers analysed blood samples collected in 1994 from adults recently vaccinated against influenza to see how their immune systems responded to flu strains that appeared over the next 30 years, including influenza A (H1N1, H3N2) and influenza B.
Dr Isabelle Foo, co-first author from the University of Melbourne, said the study found that seasonal flu shots train the immune system to recognise parts of the virus that don’t change much. This helps memory B cells “remember” past infections and respond to future H1N1 and influenza B strains.
However, the immune system struggled with rapidly changing H3N2 strains, showing why some flu types remain hard to protect against and why yearly vaccination is important.
The study also found age matters: older adults (60–75 years) had more mature antibody responses that could recognise a wider range of flu strains, including the 2009 pandemic H1N1, thanks to lifelong exposure to influenza. Both young and older adults generated strong responses, with prior exposure influencing how broadly their immune systems could react.
Professor Katherine Kedzierska, Head of the Human T Cell Laboratory at the Doherty Institute, said this is the first study to look back in time to understand long-term immunity against influenza.
“Our findings highlight how vaccines today can shape protection for decades, and why new vaccines are needed to target fast-mutating strains and improve pandemic preparedness,” she said.
The research will help guide the design of improved influenza vaccines to better protect communities against seasonal outbreaks and future pandemics.
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Source: Doherty Institute, University of Melbourne