A Dose-finding Study of a Wild-type Influenza A(H3N2) Virus in a Healthy Volunteer Human Challenge Model

Abstract

Background: The development of vaccines and therapeutics has relied on healthy volunteer influenza challenge studies. A validated human infection model with wild-type A(H1N1)pdm09 was reported previously. Our objective was to characterize a wild-type influenza A/Bethesda/MM1/H3N2 challenge virus in healthy volunteers.

Methods: Participants received a single dose of a cell-based, reverse-genetics, Good Manufacturing Practices-produced wild-type influenza A(H3N2)2011 virus intranasally and were isolated at the National Institutes of Health Clinical Center for ≥9 days. Dose escalation was performed from 104 to 107 TCID50 (50% tissue culture infectious dose). Viral shedding and clinical disease were evaluated daily.

Results: Of 37 participants challenged, 16 (43%) had viral shedding and 27 (73%) developed symptoms, with 12 (32%) participants experiencing mild to moderate influenza disease (MMID), defined as shedding and symptoms. Only participants receiving 106 and 107 TCID50 experienced MMID at 44% and 40%, respectively. Symptom severity peaked on day 3, whereas most viral shedding occurred 1-2 days after challenge. Only 10 (29%) participants had a ≥4-fold rise in hemagglutination inhibition antibody titer after challenge.

Conclusions: The A/Bethesda/MM1/H3N2 challenge virus safely induced MMID in healthy volunteers, but caused less MMID than the A(H1N1)pdm09 challenge virus even at the highest dose. There was less detection of shedding though the incidence of symptoms was similar to A(H1N1)pdm09. Fewer serum anti-hemagglutinin (HA) antibody responses with less MMID indicate that preexisting immunity factors other than anti-HA antibody may limit shedding in healthy volunteers. This A/Bethesda/MM1/H3N2 challenge virus can be utilized in future studies to further explore pathogenesis and immunity and to evaluate vaccine candidates.

Clinical trials registration: NCT02594189.

Keywords: H3N2; challenge; healthy volunteer; influenza A.

Published by Oxford University Press for the Infectious Diseases Society of America 2019.

Figures

Figure 1.

Study enrollment. One hundred ninety-seven participants were screened, with 65 (33%) having hemagglutination inhibition titers ≥1:40, making them ineligible for the study. A total of 49 participants were enrolled. Eight were excluded prior to challenge. Forty-one participants were inoculated with 1 of 4 doses of influenza A(H3N2). Four were excluded due to infection with another respiratory virus, resulting in a total of 37 participants included in the analysis. Abbreviations: echo, echocardiogram; HAI, hemagglutination inhibition; PFT, pulmonary function test; TCID50, 50% tissue culture infectious dose.

Figure 2.

A, Average Influenza Patient-Reported Outcome (FLU-PRO) total scores reported by each dose group. Participants completed FLU-PRO questionnaires daily starting on day –1 through day 14 (only day –1 through day 10 are shown). Symptoms were reported by all dose groups, although the highest severity was reported by the highest dose group of 107 50% tissue culture infectious dose. B, Types of symptoms reported by participants using FLU-PRO. For each question, participants reported 0 (none) to 4 (most severe), with a maximum daily total score and a maximum daily domain score of 4. On average, the nose scores were most severe overall, with the peak of throat and nose scores occurring on days 2 and 3, respectively. Point estimates represent means. Abbreviations: FLU-PRO, Influenza Patient-Reported Outcome; TCID50, 50% tissue culture infectious dose.

Figure 3.

Disease severity measures, by days of shedding and symptoms and by number of symptoms. A, Participants underwent daily nasal washes after challenge to identify the presence of influenza A(H3N2) after challenge. There was no viral shedding in the lowest 50% tissue culture infectious dose groups. The median duration overall for all shedders was 2 days and the median duration of viral shedding in the 2 highest TCID50 dose groups was 1 day. B, Study clinicians assessed clinical symptoms daily. Participants in all TCID50 dose groups experienced influenza symptoms with a median duration of 5 days for all participants. C, The highest number of symptoms occurred among the highest TCID50 dose group with a median of 3.5 symptoms over the study period. Lines represent medians with error bars representing the interquartile range. Abbreviations: TCID50, 50% tissue culture infectious dose.

Figure 4.

Proportion of participants with viral shedding by dose group and symptom severity. A, Participants receiving 104 or 105 TCID50 did not have any viral shedding. Participants receiving 106 and 107 TCID50 had the highest proportion of shedding 1 day after challenge and no shedding by day 7. B, Participants completed daily FLU-PRO questionnaires indicating type and severity of symptoms. The maximum daily score (most severe) is 4. The peak of average symptom severity by FLU-PRO occurred on day 3, with the most severe symptoms being reported on days 1–3. C, Study clinicians evaluated symptoms daily during the inpatient stay. The number of symptoms by day ranged from 0 to 12, with the average number of symptoms peaking on day 3. D, FLU-PRO total scores and number of symptoms had similar trajectories. Circles and triangles represent means and the error bars represent standard errors of the mean. Abbreviation: FLU-PRO, Influenza Patient-Reported Outcome; TCID50, 50% tissue culture infectious dose.

Figure 5.

Hemagglutination inhibition (HAI) and neuraminidase inhibition (NAI) titers. HAI and NAI titers were evaluated pre- and postchallenge and in follow-up. A, There was an overall increase in HAI titers among all participants by week 8 compared to day 0 (prechallenge). B, NAI titers were elevated even prior to challenge and remained elevated throughout the study period. C, Participants were grouped by response after challenge. Those participants with a response after challenge had a ≥4-fold increase in HAI titer after challenge and showed a significant rise by week 8. D, Many participants did not have a rise in HAI titer after challenge, and HAI titers remained low throughout the study period. Dotted lines indicate the lowest level of detection. Dashed lines indicate the level of protection (≥1:40). Lines represent geometric mean titers and error bars represent 95% confidence intervals. Abbreviations: HAI, hemagglutination inhibition; NAI, neuraminidase inhibition.