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23 Feb 2022

Influenza virus infection history shapes immune responses to the seasonal flu vaccination

Researchers at the Doherty Institute have shown that individuals with prior exposure to influenza infection are likely to produce a better immune response to the seasonal flu vaccination.

The study which followed 100 participants over a nine-year period, showed that the individuals who had contracted influenza responded better to the vaccines, producing higher levels of antibodies than those who had not.

Seasonal influenza is estimated to cause up to 645,000 deaths annually and affects millions of people world-wide.

In Australia, annual influenza vaccination is recommended for people at higher risk of severe influenza.

Influenza vaccines contain four strains representing A(H1N1), A(H3N2), B Victoria and B Yamagata viruses that circulate in the community.

Vaccines are re-formulated annually to keep pace with virus evolution however despite relatively frequent replacement of A(H3N2) strains, vaccine effectiveness against this subtype is particularly poor.

In this study, a cohort was established in Vietnam and monitored for an unprecedented nine-year period, with both symptomatic and asymptomatic infections being recorded.

Vaccine responses were then assessed by measuring antibodies against 40 A(H3N2) viruses representing strains that have circulated since A(H3N2) viruses emerged in humans.

Lead author on the paper Dr Annette Fox, a Senior Research Scientist at the WHO Collaborating Centre for Reference and Research on Influenza at the Doherty Institute explained that the 72 participants who had at least one A(H3N2) virus infection not only had higher antibodies on average than the 28 who hadn’t been infected, but they were also less likely to develop symptomatic infection following vaccination.

“These people who developed symptomatic infection had much stronger antibody responses to infection than to vaccination,” Dr Fox explained

“The range of A(H3N2) viruses recognised by vaccine-induced antibodies was associated with the prior infection strain.

“This suggests that the recall of immunological memory induced by prior infection enhances antibody responses to inactivated influenza vaccine and is important to attain protective levels of antibodies.”

The team are now investigating which specific characteristics of memory B cells induced by infection drive robust antibody responses, and could be harnessed to improve vaccine effectiveness against A(H3N2) viruses.

The cohort in Vietnam was established in collaboration with Oxford University and the Viet Nam National Institute of Hygiene and Epidemiology