a, The Ct values of ORF1b and N obtained with RT–PCR that were detected in nasopharyngeal swabs from asymptomatic (n = 37) and symptomatic (n = 37) groups. The box plots show the medians (middle line) and the first and third quartiles (boxes), whereas the whiskers show 1.5× the IQR above and below the box. Unpaired, two-sided Mann–Whitney U test P values are depicted in the plots, and the significant P value cutoff was set at 0.05. b, The Kaplan–Meier method was used to estimate the positive rate of viral RNA, and the two-sided log-rank test was applied to evaluate the significance difference of the duration of viral shedding in the symptomatic and asymptomatic groups.