Mean counts and percentages of all T-and B-lymphocyte subsets increased after 3 days of illness compared with results obtained during the fi rst 3 days of illness ( Figure 1 ). However, the increase in CD8 and B cells was not signifi cant. Another study showed a decrease in CD4, CD8, and B cells ≤2 days of symptom onset in patients with pandemic (H1N1) 2009 than in healthy persons (4). Our results show impaired adaptive immune responses and a gradual increase during recovery in mildly affected patients. We measured serum cytokine concentrations and hemagglutination inhibition (HAI) antibody titers in patients during hospitalization and the follow-up period ( Figure  2 ). We observed an increase in interleulin-6 (IL-6) levels 1 day after illness onset, which were 6.0-fold higher than the baseline level, and a 2.3-fold increase in interferon-γ (IFN-γ) levels. These levels decreased to baseline levels 5 days after illness onset, although the IL-6 level 5 days after illness onset was higher than levels 15 and 37 days after illness onset. The maximum IL-10 level 1 day after symptom onset was 3.2-fold higher than the baseline level. This level decreased to a value lower than the baseline level within 4 days, and then gradually increased to the baseline level 37 days after illness onset. Serum IL-6, IFN-γ, and IL-10 levels were not related to patient temperature 1 day after symptom onset, peak temperature during the disease, or period of fever. These levels showed minor differences that were not related to cough or sore throat in patients.