Background: COVID-19 can be severe in children with acute leukaemia (AL), significantly delaying chemotherapy. This is the first study to address the safety and immunogenicity of BNT162b2 in children with AL.
Methods: The PACIFIC trial (NCT04969601) was a phase 1/2 dose-finding study in children aged <15 years with AL and their siblings. Two doses of BNT162b2 vaccine were administered 21 days apart. The co-primary endpoints were safety, assessed by dose-limiting toxicity, and humoral immunogenicity, defined by an anti-Spike IgG titer ≥260 BAU/ml one month after the second injection. A third dose of vaccine was administered to children with an anti-Spike IgG titer <260 BAU/ml. Humoral and cellular immune responses were assessed for 12 months after the first vaccine injection.
Results: Sixty-one patients and 15 siblings were included. No toxicity was observed during dose escalation. Thus, 44/53 children received the 30 μg vaccine dose. Two months after the first injection, the humoral response was lower in patients than siblings (52 % vs 100 %, p < 0.001), whereas the T-cell response was similar in the two groups (80 % versus 100 %, p = 0.1). A significant humoral response was observed in 43 % of patients after the third dose. Both humoral and Covid-19-specific T-cell responses persisted for at least one year after vaccination. No severe Covid-19 occurred during the study.
Conclusions: Vaccination of children with acute leukaemia with adult doses (30 μg) of BNT162b2 is well tolerated and results in significant T-cell response children with AL, even during chemotherapy. As doses of 10 μg is currently recommended for children, these results support the value of increasing vaccine doses in immunocompromised patients.
Keywords: Acute leukaemia; Children; Covid-19; Vaccine; mRNA.
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