ABSTRACT
BACKGROUND: The BNT162b2 mRNA COVID-19 vaccine has been administered to children and adolescents with cancer and hematologic diseases since they are at high risk of manifesting severe symptoms if they have COVID-19 infection but the adequate immune response after vaccination in these immunocompromised patients are questionable. OBJECTIVE: To evaluate the immune response of children and adolescents with cancer and hematologic diseases after receiving 2 doses of the BNT162b2 mRNA COVID-19 vaccine. METHODS: This is a prospective cohort study of patients with cancer and hematologic disease, who aged 12- 18 years old and received 2 doses the BNT162b2 vaccines at 4 weeks apart were enrolled. Immunogenicity was determined by measuring serum anti-SARS-CoV-2 immunoglobulin antibodies directed against the receptor binding domain (RBD) of S1 domain of the spike protein (Anti S-RBD), surrogated viral neutralization test (sVNT) of SARS-CoV-2 and Delta strain. Blood samples were collected and analyzed at 4 and 12 weeks after vaccination. The seroprotective rate was defined as sVNT ≥ 68%. RESULTS: From Oct 2021 to Jan 2022, 43 children were enrolled, 21 were on-therapy and 22 were off-therapy. 25 were hematologic malignancy, 15 solid tumor and 3 hematologic diseases with immunosuppressive drugs. The GMT (95%CI) of a anti S-RBD IgG level at 4 weeks after vaccination were 56.05 (13.2,238.2) and 3633 (2689,4908) BAU/mL in on-therapy and off-therapy group, respectively, p<0.001. The sVNT (95%CI) of delta strain were 26% (5.85-73.55%) and 97.05% (96.0-97.4%) as the seroprotective level which were 33.3% in on-therapy group and 100% in off-therapy group (p<0.001). 14 children in on-therapy group need an additional dose. CONCLUSION: After complete vaccination, the seroprotective rate and antibody level in pediatric and adolescent patients with cancer and hematologic disease who receive immunosuppressive agents are quite low, compared with patients who had complete treatment. Additional dose of primary series should be offered.