Characterisation of a wild-type influenza (A/H1N1) virus strain as an experimental challenge agent in humans

Abstract

Background: Human challenge models using respiratory viruses such as influenza are increasingly utilised in the development of novel vaccines and anti-viral modalities and can provide preliminary evidence of protection before evaluation in field trials. We describe the results of a clinical study characterising an A/H1N1 influenza challenge virus in humans.

Methods: The challenge agent, influenza A/California/2009 (H1N1), was manufactured under cGMP conditions and characterised in accordance with regulatory guidelines. A dose-ascending open-label clinical study was conducted in 29 healthy young adults screened sero-negative to the challenge strain. Subjects were intranasally inoculated with three increasing doses of virus and physician-reported signs, subjected-reported symptoms, viral shedding and immunological responses were monitored.

Results: A dose-dependent increase in clinical signs and symptoms was observed with 75% of subjects developing laboratory-confirmed illness at the highest inoculum (3.5 × 10(6) TCID50). At the highest dose, physician or subject-reported signs of infection were classified as mild (all subjects), moderate (50%) and severe (16%) with peak symptoms recorded four days after infection. Clinical signs were correlated with nasal mucus weight (P < .001) and subject-reported symptoms (P < .001). Geometric mean peak viral shedding was log10 5.16 TCID50 and occurred three days after inoculation with a median duration of five days. The safety profile was such that physiological responses to viral infection were mainly restricted to the upper airways but were not of such severity to be of clinical concern.

Conclusions: A highly characterised wild-type Influenza A/California/2009 (H1N1) virus manufactured for clinical use was shown to induce a good infectivity profile in human volunteers. This clinical challenge model can be used for evaluating potential efficacy of vaccines and anti-viral therapeutics.

Trial registration: NCT02014870.

Figures

Figure 1

Summary of clinical, virological and immunological responses. Data from individual subjects is ranked per cohort according to physician-reported signs. Physician-reported signs: Data is shown as the cumulative number of clinical signs reported after influenza challenge during the quarantine period. For each subject, mild, moderate and severe clinical signs are shown as a stacked bar graph with no weighting of data applied. Fever of greater than 37.7°C is shown as a symbol next to the bar where appropriate. Subject-reported symptoms: As for clinical signs but reporting the sum of the subject-reported symptoms. Nasal discharge weight: Data is shown as the cumulative nasal discharge weight in grams. Lymp:Monocyte ratio: The lymphocyte to monocyte ratio was calculated from haematology results collected 5 days after infection. Viral shedding (rRT-PCR): The results are shown as the cumulative virus copies/mL during the quarantine period. Serology: Geometric mean HI titres to A/California/7/2009 are shown from serum samples collected at 28 days after challenge. HI tires at screening and one day prior to challenge were all negative (≤10).

Figure 2

Kinetics of Virus Shedding in infected subjects. Viral shedding was measured in nasal wash samples collected daily during the quarantine period by means of rRT-PCR. A virtual quantification tool was applied to the rRT-PCR Ct values to generate an estimate of viral copy number [14]. The graph shows the mean copy number + SEM from subjects who became infected.

Figure 3

Kinetics of clinical illness and virus infectivity. A. The clinical symptom score, nasal discharge weight (g) and virus shedding by TCID50 are presented across the quarantine period for subjects in cohort 3 only (N = 12). Data is shown as mean ± SEM.