A Multi-Center, Controlled Human Infection Study of Influenza A (H1N1)pdm09 in Healthy Adults

Abstract

ABSTRACTBackgroundInfluenza controlled human infection model (CHIM) studies can advance development of vaccines and therapeutics. Our objective was to evaluate the associations between baseline challenge virus-specific hemagglutination inhibition (HAI) and microneutralization (MN) titers and subsequent symptomatic influenza virus infection.MethodsWe enrolled healthy adults aged 18 through 49 years in a multisite CHIM study using influenza A/Bethesda/MM2/H1N1, an A/California/04/2009/H1N1pdm-like virus (NCT04044352). We excluded persons vaccinated against influenza within the previous six months. We collected serial safety labs, serum for HAI and MN, and nasopharyngeal swabs for RT-PCR testing. Analyses used the putative seroprotective titer of ≥40 for HAI and MN. The primary clinical outcome was mild-to-moderate influenza disease (MMID), defined as ≥1 post-challenge positive qualitative RT-PCR test with a qualifying symptom/clinical finding.FindingsOf 76 participants given influenza virus challenge, 54 (71.1%) experienced MMID. Clinical illness post-challenge was generally very mild. MMID attack rates among participants with baseline titers ≥40 by HAI and MN were 64.9% and 67.9%, respectively, while MMID attack rates among participants with baseline titers <40 by HAI and MN were 76.9% and 78.3%, respectively. The estimated odds of developing MMID decreased by 19% (odds ratio=0.81; 95% CI: 0.62, 1.06; p=0.126) for every two-fold increase in baseline HAI. There were no deaths, serious adverse events, or other significant adverse events.InterpretationIn a multi-site influenza CHIM study, we assured the safety of our participants and achieved a 71.1% attack rate of MMID. High baseline HAI and MN were associated with protection from illness.