Figure 2. Transmission competitiveness of Delta and Omicron in a naïve hamster population.

Chain transmission in naïve Syrian hamsters assessing the competitiveness of Delta and Omicron over three transmission events. A. Donor animals (N = 6) were inoculated with a total of 10⁴ TCID₅₀ of Delta and Omicron (1:1 ratio) via the IN route, and three groups of sentinels (sentinels 1 (N = 6), 2 (N = 6) and 3 (N = 4)) were subsequently exposed. Half were exposed by direct contact (housed in the same cage), and half at 16.5 cm distance (airborne exposure). Animals were exposed at a 1:1 ratio; exposure occurred 24h post inoculation (Donors → sentinels 1) and 48h post exposure for subsequent groups (sentinels → sentinels). B. Summary of infection status for the donors and sentinels. Oropharyngeal swabs were taken on 2, 3, and 5 DPI/DPE, and lungs and nasal turbinates were collected at day 5 DPI/DPE. Individuals were considered infected, if 2 out of 5 samples were positive for sgRNA (oral swab, lung or nasal turbinate). Bar charts depict summary of individuals, divided into contact and airborne chains. C. The receptor binding domain of the SARS-CoV-2 spike was sequenced for all sgRNA positive swabs collected at 2, 3, and 5 DPI/DPE. Heatmap representing all sgRNA positive swab samples from each individual for each chain and showing the percentage of Delta detected. Colors refer to legend on right (D = donor, S = sentinel), grey = no sgRNA present in the sample or sequencing unsuccessful. D. Overall percentage of Delta and Omicron in all sgRNA positive samples in each group, separated by sample type. Bar charts depicting median and 95% CI. Number of sgRNA positive samples over all samples analyzed is indicated on top. Yellow = Delta, purple = Omicron.