(A) Comparison of the titers of neutralizing antibody in different groups. (B) Comparison of the titers of neutralizing antibody in different subgroups of asymptomatic individuals and mild patients with that of healthy contacts. (C) The dynamic change of the titers of neutralizing antibody over time.

Lines indicate change of neutralizing ability at different times after exposure (asymptomatic cases and healthy contacts) or after symptom onset (mild cases). Samples with neutralizing titers below 1:10 were plotted at the dotted line (log2NT50=1). Statistical significance in A and B was determined using unpaired t-test, horizontal bars indicate mean and SD.