Lymphocyte subsets in peripheral blood of patients
According to the results of each index, CD4+ T and CD8+ T cells were divided into below the normal values, within the normal value and above the normal values. The corresponding quantities and proportions were respectively calculated based on age, and the results were shown in Table 2.
Compared with mild pneumonia children, patients with severe pneumonia had a higher count of CD8+ lymphocyte, while a lower percentage of CD4+ lymphocyte was observed. However, there were no significant differences in the percentage of CD4+ and CD8+lymphocytes between the two groups (p-value= 0.3 and p-value= 0.4, respectively) (Figure 1).

CD4+/CD8+T cell ratio and COVID-19 Severity

Interestingly, the severe group had a significantly lower CD4+/CD8+ T cell ratio compared to the mild group (1.1 ± 0.47 vs. 1.4 ± 0.8, p value: 0.039) (Figure 1).
CD4+/CD8+ less than 2, 1.5, and 1 was found in 48 (87%), 40 (73%), and 19 cases (35%) , respectively. The frequency of an inverted CD4+/CD8+ ratio increased with age. A ratio<1 was seen in 32% of patients less than 5 years (n=6) and in 68% of 5- to 15-year-olds (n=13). Males were more likely to have a decreased ratio than females (Table 3).
Among 7 cases who died, 100% had CD4+/CD8+ ratio<2, 86% had CD4+/CD8+ ratio<1.5, and 29% had CD4+/CD8+ratio<1.