Feasibility and Safety of Aerosolized Influenza Virus Challenge in Humans Using Two Modern Delivery Systems

Controlled human infection models are widely used to study infectious diseases. Since the 1960s, these studies have primarily relied on intranasal inoculation, as earlier aerosol-based methods raised safety concerns and were largely abandoned despite better mimicking the natural route of infection.

Utilizing modern advances in aerosol delivery, we conducted a dose-escalation study to evaluate the safety and feasibility of aerosol inoculation for human influenza challenge. Healthy adults aged 18-49 years were inoculated with influenza A/Perth/16/2009 (H3N2) using either a flow-focusing monodisperse aerosol generator (FMAG) delivering coarse particles or a medical nebulizer delivering fine particles. Participants were monitored in a controlled inpatient setting with symptom tracking, virologic sampling, and serology. Doses were escalated according to predefined safety and attack rate thresholds.

Fourteen participants were enrolled. Flow-focusing monodisperse aerosol generator delivery at higher dose levels resulted in infection in 75% of participants (3/4), while nebulizer delivery produced infection in 50% (2/4). Illnesses were mild and self-limited. Viral shedding was detected at multiple respiratory sites, and adverse events were infrequent and generally mild. No serious adverse events occurred. Antibody responses were observed in a subset of infected participants.

In this small pilot, aerosolized challenge using modern delivery systems was feasible under controlled conditions; no safety concerns were identified, and MMID was induced in a subset of participants. These data establish a methodological framework for future studies evaluating pathogenesis and mucosal immune responses to a variety of respiratory pathogens.