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Updated: Jul 23, 2025
An Optimized Hemagglutination Inhibition HI Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Safety and Immunogenicity of a Delayed Heterologous Avian Influenza A(H7N9) Vaccine Boost Following Different Priming
Hana M El Sahly1,2, Inci Yildirim3, Sharon E Frey4
1Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA.
Background:
Influenza A (H7N9) has caused multiple disease waves with evidence of strain diversification. Optimal influenza A (H7N9) prime-boost vaccine strategies are unknown.
Methods:
We recruited participants who had received monovalent inactivated A/Shanghai/2/2013 (H7N9) vaccine (MIV) approximately 5 years earlier, as follows: MIV with MF59 (MF59 × 2 group), MIV with AS03 (AS03 × 2 group), unadjuvanted MIV (No Adj group), MIV with MF59 or AS03 followed by unadjuvanted MIV (Adjx1 group), and A/H7-naive (unprimed group). Participants were randomized to receive 1 dose of AS03-adjuvanted or unadjuvanted A/Hong Kong/125/2017 (H7N9) MIV and were followed for safety and immunogenicity using hemagglutination inhibition (HAI) and neutralizing antibody assays.
Results:
We enrolled 304 participants: 153 received the adjuvanted boost and 151 received the unadjuvanted boost. At 21 days postvaccination, the proportion of participants with HAI antibody titers against the boosting vaccine strain of ≥40 in the adjuvanted and unadjuvanted arms, respectively, were 88% and 49% in MF59 × 2 group, 89% and 75% in AS03 × 2 group, 59% and 20% in No Adj group, 94% and 55% in Adjx1group, and 9% and 11% in unprimed group.
Conclusions:
Serologic responses to a heterologous A(H7N9) MIV boost were highest in participants primed and boosted with adjuvant-containing regimens.
Clinical Trials Registration:
NCT03738241.
