Comparison of the immunogenicity of adjuvanted and conventional egg-based quadrivalent influenza vaccines among healthcare personnel in Lima, Peru: A randomized controlled trial

Objectives We conducted a randomized controlled trial to evaluate whether adjuvanted quadrivalent inactivated influenza vaccine (aIIV4) generates superior immunogenicity against influenza viruses compared to conventional quadrivalent inactivated influenza vaccine (IIV4) among healthcare personnel (HCP) in Lima, Peru. Methods During 2022-2023, we randomized 192 HCP aged ≥18 years to receive 2022 Southern Hemisphere IIV4 or aIIV4 and collected pre-, 1-month post-, and 6-months post-vaccination sera. Geometric mean titers (GMTs), GMT ratios, seroconversion rates (SCR), and seroprotection rates (SPR) were compared against vaccine reference viruses—influenza A(H1N1)pdm09, A(H3N2), B/Victoria, and B/Yamagata—using hemagglutination inhibition assays. Results Most HCP (77-99%) had titers ≥40 following vaccination. One-month post-vaccination, aIIV4 induced higher GMTs (GMT ratio: 1.7 [95% confidence interval 1.1-2.7]) and SCR (88.4% [80.4-93.4] vs 62.1% [52.1-71.2]) against A(H1N1)pdm09 and higher SCR (82.1% [73.2-88.5] vs 62.1% [52.1-71.2]) against A(H3N2) compared to IIV4. At 6 months, aIIV4 induced higher SPR against A(H3N2) (90.4% [82.8-94.9] vs 74.0% [64.4-81.7]) than IIV4. IIV4 recipients vaccinated the preceding influenza season had lower odds of seroconverting to A(H1N1)pdm09 compared to IIV4 recipients who were not vaccinated (adjusted odds ratio: 0.29 [0.13-0.63], P = 0.002). Conclusion These findings provide insights into the benefits of an enhanced influenza vaccine (aIIV4) to help overcome the immune blunting effects of repeat vaccination among HCP.