Figure 2. The SARS-CoV-2 spike N501Y mutant has a consistent advantage in competitions with wt during the upper airway replication and transmission between hamsters.

a,b, Results of the competition between spike N501Y mutant and the wt assessed by sampling nasal washes of both donor (a) and recipient hamsters (b) from 1–4 days post-inoculation (donors) or post-contact (recipients). c,d, Results of the competition between the N501Y mutant and the wt in the tracheae of both donor (c) and recipient hamsters (d) at 2- or 4-days post-inoculation or post-contact. e,f, Results of the competition between the N501Y mutant and the wt in the lungs of both donor (e) and recipient hamsters (f) sampled 2- or 4-days post-inoculation or post-contact. g-i, The ratios in the competitors in the nasal washes (g), tracheae (h) and lungs (i) of recipient hamsters were compared to the ratio of N501Y:wt measured from the day 1 nasal wash of donor hamsters (representing the virus population transmitted) to assess changes corresponding to transmission versus replication in the recipient hamsters. a-i, The fitness advantage of the N501Y substitution against wt both during infection (donor data) and after transmission of the virus to recipients is shown by the significant changes in ratios between the harvested samples and inocula. Red dots represent individual animals (n=5), the horizontal lines in each catseye represent the mean, shaded regions represent standard error of the mean; y-axes use a log₁₀ scale. Black numbers above each set of values (catseye) indicate the relative fitness estimates. P values are calculated for the group (strain) coefficient for each linear regression model. *p<0.05; **p<0.01; ***p<0.001.