Fig. 2. Infection with WA1/2020 SARS-CoV-2 provides natural protection from homologous or heterologous strain rechallenge-induced weight loss.

(A) Hamsters (n = 18) were challenged on day 0 with 5 × 10⁴ TCID₅₀ (in 100 μl) of WA1/2020 SARS-CoV-2 challenge stock by the intranasal route and monitored for 35 days after challenge. Average relative body weight after primary challenge displayed as means ± SEM. (B) At week 5, hamsters were divided into three groups and rechallenged with 5 × 10⁴ TCID₅₀ of WA1/2020 (group 1, n = 6), B.1.1.7 (group 2, n = 5), or B.1.351 (group 3, n = 6) SARS-CoV-2. In addition, three groups of naïve hamsters (n = 6 per group) were challenged on study day 35 with the matched strains and doses (groups 4 to 6). (C) To allow comparison of weight loss after SARS-CoV-2 challenge or re-challenge on day 35, for the remainder of the study, hamster weights were normalized to the weight on study day 35. Average relative weight after primary challenge (open symbols) or rechallenge (closed symbols) is indicated as means ± SEM. (D) Peak weight loss over the span of study days 35 to 49 is shown. Maximum weight loss of each hamster is displayed, with group means indicated by horizontal lines. (E and F) At the terminal time point, day 49, hamsters were euthanized, and lung tissue was collected to quantify sgRNA (E) and gRNA (F) viral RNA. Log-transformed viral loads in individual hamsters, normalized per gram of lung tissue, are displayed. Horizontal lines indicate group means.