Influenza vaccine responses differ between young children previously exposed to influenza antigens via infection versus vaccination

Area of Science:

• Immunology
• Pediatrics
• Vaccinology

Background:

• Annual influenza vaccination is recommended for children.
• The impact of early life influenza exposure (infection vs. vaccination) on subsequent immunity is not well understood.
• This study investigates how prior influenza A(H3N2) infection versus vaccination influences immune responses to subsequent influenza vaccination in young children.

Purpose of the Study:

• To examine the effect of early life influenza A(H3N2) infection versus vaccination on subsequent antibody responses to influenza vaccination.
• To compare antibody titres and seroconversion rates after vaccination in children with different prior influenza exposure histories.

Main Methods:

• Pilot study involving 19 children aged 6-60 months in Australia (2019-2021).
• Plasma collected pre- and post-vaccination over up to three years.
• Antibody titres measured using hemagglutination inhibition (HI), neuraminidase inhibition (NI) assays, and ELISA.
• Children classified based on prior vaccination or influenza A(H3N2) infection history.

Main Results:

• Post-vaccination antibody titres and titre-rises against A(H3N2) were significantly higher in children with prior infection compared to prior vaccination.
• Seroconversion rates for A(H3N2) were 8/8 in the prior infection group versus 3/7 in the prior vaccination group.
• Antibody responses to A(H1N1) did not differ significantly between groups.

Conclusions:

• Prior influenza A(H3N2) infection may be superior to vaccination in priming subsequent vaccine antibody responses against A(H3N2).
• Findings suggest a potential difference in immunological imprinting based on the type of early influenza exposure.