Fig 1.
(a) Schematic of the study workflow and exposure event room. (b) Timelines for cohorts 24b (started January 24, 2024) and 24c (started February 14, 2024). Shaded blocks indicate phases (Run-in, Donor exposure, Observation, Discharge, Follow-up). Arrows mark donor introductions (D24b-1 on 01/30; D24c-1 on 02/16, D24c-2 on 02/17, D24c-3&D24c-4 on 02/21).
Table 1.
Recipients demographics for cohorts 24b & 24c.
Table 2.
Donor demographics for cohorts 24b & 24c.
Fig 2.
Variations in indoor temperature, relative humidity, and CO2 concentration in the exposure event room and hallway during cohorts.
(a) Cohort 24b (Jan 30–Feb 1, 2024); (b) Cohort 24c, first donor block (Feb 16–19, 2024); (c) Cohort 24c, second donor block (Feb 21–23, 2024). The left y-axis shows temperature (°C) and relative humidity (%); the right y-axis shows CO2 concentration (ppm). Line plots show temperature (orange, solid), relative humidity (dark blue, solid), exposure event room CO2 (green, dashed), hallway CO2 (purple, dot-dashed). Yellow bands denote each exposure event windows; vertical ticks mark exposure start (red) and end (black). Temperature and humidity were maintained within stable ranges by the mechanical systems, as these parameters can influence virus stability. CO2 concentration is a proxy for ventilation and a direct indicator of rebreathed air; levels increased during exposure events due to occupancy and slowly returned to background afterward, reflecting the low ventilation condition targeted in these experiments.
Fig 3.
Viral RNA and infectious viral load in Donor samples.
Violin plots depict the distribution of viral RNA and infectious (fluorescent focus unit, FFU) viral loads (log10 RNA copies and FFU) across four different sample types: breath aerosol <5 µm, breath aerosol ≥5 µm, mid-turbinate swabs (MTS), and saliva. RNA copy and FFU values are expressed as follows: per 30-minute sample for breath aerosols, per swab for MTS, and per mL for saliva. Negative samples were assigned a value of 1.
Fig 4.
Donor sample viral RNA, infectious viral load, total symptom score and cough trajectories with timing of positive environmental samples.
Each individual plot shows one donor over their days in quarantine. Lines/points show RNA (solid) and FFU (dashed) for: breath aerosol <5 µm (solid circle, orange), breath aerosol ≥5 µm (solid triangle, sky blue), mid-turbinate swab (MTS; solid square, green), and saliva (solid diamond, purple). Cough counts during 30-min breath sampling (dot-dash line, black, open circle) and self-reported total symptom score (dotted line, grey, open square) are overlaid and referenced to the right axis. Shaded bands mark environmental positives centered on the day that positives samples were detected: Ambient+ (light blue) and Ambient + & Surface+ (yellow). Donors’ samples were collected once per day, prior to any exposure events (on the afternoon or evening of admission and otherwise in the morning), ambient samples were collected during afternoon events and surface swabs at the end of each exposure event. RNA copy and FFU values are expressed as follows: per 30-minute sample for breath aerosols, per swab for MTS, and per mL for saliva. Negative samples were assigned a value of 1.
Fig 5.
Symptom severity and progression in Donors during quarantine.
(a) Heatmap shows the maximum individual symptom scores reported by individual Donors. The color intensity represents the symptom severity, with scores ranging from 0 to 3. Symptoms are listed along the x-axis, and Donors are on the y-axis. Columns are grouped by domains: Upper respiratory (running nose, stuffy nose, sneeze, sore throat, earache), Lower respiratory (chest tightness, shortness of breath, cough), and Systemic (malaise, headache, muscle & joint ache, chills, feverish). (b) Line plots present total symptom scores and symptom group scores (upper respiratory, lower respiratory, and systematic symptoms) over time for each individual Donor. The x-axis represents cohort timelines, and the y-axis indicates the sum of each symptom group scores.
Fig 6.
Symptom severity and progression in Recipients during quarantine.
(a) Heatmap shows the maximum individual symptom scores reported by individual Recipients. The color intensity represents the symptom severity, with scores ranging from 0 to 3. Symptoms are listed along the x-axis, and Recipients are on the y-axis. (b, c) Line plots present total symptom scores over time for Recipients. (b) shows data for the Recipients in cohort 24b, while (c) shows data for those in cohort 24c. The x-axis represents the timeline, with the yellow-shaded areas indicating periods of Donor quarantine. Each subplot corresponds to an individual Recipient, with blue lines (circle) representing the control group and green lines (triangle) representing the intervention group.
Fig 7.
HAI titers over time for Donors and Recipients in Cohort 24b.
HAI titers are shown for Donors (solid lines, star symbols), Vaccinated Recipients (dot-dashed lines, filled triangles), and Unvaccinated Recipients (dot-dashed lines, open circles) at four time points: T0 (Recipient screening), T1 (Admission), T2 (Discharge), and T3 (Follow-up). Virus targets are color-coded: A/Victoria/4897/22 (H1N1, blue), A/Darwin/6/21 (H3N2, green), and B/Austria/1359417/21 (red). Each facet represents an individual study participant.
Fig 8.
HAI titers over time for Donors and Recipients in Cohort 24c.
HAI titers are shown for Donors (solid lines, star symbols) and Unvaccinated Recipients (dot-dashed lines, open circles) at four time points: T0 (Recipient screening), T1 (Admission), T2 (Discharge), and T3 (Follow-up). Virus targets are color-coded: A/Victoria/4897/22 (H1N1, blue), A/Darwin/6/21 (H3N2, green), and B/Austria/1359417/21 (red). Each facet represents an individual study participant.