Childhood flu exposure impacts your immune response later

Australian and US researchers, led by Dr Marios Koutsakos from The Peter Doherty Institute for Infection and Immunity, have discovered that people develop stronger immune responses to the variants of influenza B they were exposed to during their childhood. This early exposure to the virus impacts how well their immune system can recognise new variants and protect against them.

Previous epidemiological studies have noted differences in susceptibility and severity of influenza infections based on year of birth, suggesting a link between childhood exposure to influenza and subsequent lifelong immune responses to the virus. The purpose of the new research, according to the Doherty Institute’s Peta Edler, was to provide robust immunological evidence to support these observations.

The researchers analysed samples collected from people born between 1917 and 2008 in both Australia and the United States. Specifically, they measured and compared antibodies to influenza B strains circulating globally between 1940 and 2021, with their results published in the journal Nature Microbiology.

“Using this comprehensive dataset, we discovered that the highest concentrations of antibodies in each sample generally corresponded with the dominant strain of influenza B virus that was circulating during that individual’s childhood,” Edler said. So if newer influenza B variants share similar characteristics with strains that were circulating during an individual’s first 5–10 years of life, their body will exhibit a stronger immune response than for strains with many differences.

“Essentially, when it comes to influenza B virus infections, first impressions matter,” added Edler, who was first author on the study. “The initial, early-life exposure to the virus appears to influence how the immune system responds to future influenza B viruses.”

While generally less common than influenza A infections, influenza B still accounts for a substantial proportion of cases annually, with a high morbidity and mortality burden — particularly for children and people under 18 years old. According to Koutsakos, establishing an immunological link between initial exposure to influenza B and long-term immune responses opens new pathways for vaccination and the public health response to manage these risks.

“Our research could help predict which populations are most at risk of disease during each flu season, which would guide the development of public health strategies targeting specific age groups,” Koutsakos said.

“Moving forward, we want to explore what drives this long-term immunity and find out whether our immune system behaves the same way following its first exposure to influenza A. This work could uncover potential targets for the design of new vaccines, but also inform tailored immunisation strategies.”

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