The dynamics of humoral and cellular immunity in recovered
children and adolescents
SARS-CoV-2 specific humoral immunity was found to decay over time, but
not T cell immunity (Fig. 3). Linear regression analysis showed that the
level of SARS-CoV-2 RBD IgG was significantly associated with recovery
time (p=6.31e-07, R2=0.5808) (Fig.
3A), but not with the specific CD4+ (p=0.783) or CD8+ (p=0.915) T cell
responses (Fig. 3B). SARS-CoV-2 RBD IgG had a fast decay rate (-0.0377
anti-RBD IgG ratio/day) while CD4+ (-0.0022%/day) and CD8+
(-0.0001%/day) T cell responses persist over time, including the
patient with the longest follow-up time at 219 days who had undetectable
anti-RBD IgG but persistent SARS-CoV-2 specific CD4+ and CD8+ T-cell
response. The average SARS-CoV-2 RBD IgG half-life
(t1/2) decay was 121.6 days, and the presence of
antibodies was estimated to last for 237.7 days or 7.9 months. The same
estimation was not applicable to CD4+ and CD8+ T cell responses because
of the lack of association with time.
Age is a factor associated with the measured RBD IgG level and T
cell activation magnitudes in recoveredchildren and adolescents
Fifteen patients were younger than 12 years and 16 patients were 12
years or older. The results demonstrated differences in the immune
responses to SARS-CoV-2 between older and younger
children. In comparison to
children older than 12 years, the younger patients had a significantly
higher level of SARS-CoV-2 RBD IgG ratio (p=0.041) (Fig 4A). While the
frequency of CD4+ T cells reactive to mixed M, N and S peptide pool was
similar between the age groups (Cohen’s d=0.071) (Fig 4B(i)), the
frequency of S-peptide specific CD4+ T cells was higher in younger
children (Cohen’s d=0.3058) (Fig 4B(ii)). Correlative analysis showed
that the four patients with highest level of anti-RBD IgG and S-peptide
specific CD4+ T cells were all from the younger age group (Fig 4D(i)).
In contrast, no difference was observed between the two age groups in
SARS-CoV-2 S-reactive CD8+ T cells (Cohen’s d=0.03164) (Fig 4C and
4D(ii)).