a, b, Eight-to-ten-week-old female and male K18-hACE2 transgenic mice were administered 103 FFU of the indicated SARS-CoV-2 strain by intranasal inoculation. One day later, mice received 200 μg (about 10 mg kg−1) of the indicated mAb treatment by intraperitoneal injection. Brain tissues were collected at six days after infection. Viral RNA levels are shown (a, b) (line indicates median; in order from left to right n = 9, 6, 6, 6, 6, 6 and 6 (a); n = 7, 6, 6, 6, 6, 5 and 7 (b) mice per group, two experiments; one-way ANOVA with Dunnett’s test with comparison to control mAb: ns, not significant, ****P < 0.0001). Dotted line indicates the limit of detection of the assay.