ChAdOx1 nCoV-19 Vaccine in Children Aged 6–17 Years

Quick Takes

  • This study relates findings from a phase 2 single-blind randomized trial of the ChAdOx1 nCoV-19 vaccine in children and adolescents (aged 6-17).
  • While mild local and systemic adverse events were common, there were no serious adverse events attributed to the vaccine at 28 days of follow-up.
  • The vaccine was immunogenic, with stronger humoral immunity observed in younger (6-11 years) vs. older (7-12 years) participants, and in the longer dosing interval group (112 days) vs. the shorter (28-day).

Study Questions:

Is the ChAdOx1 nCoV-19 vaccine safe and immunogenic in children and adolescents aged 6-17 years?


This study is a phase 2, single-blind, randomized, controlled trial of the ChAdOx1 nCoV-19 vaccine in children and adolescents (aged 6-17 years). Healthy participants were randomly assigned to four groups (4:1:4:1) to receive two intramuscular doses of 5 × 1010 viral particles of ChAdOx1 nCoV-19 or control, 28 days or 84 days apart. The primary outcome was assessment of safety and tolerability in the safety population. The secondary outcome was immunogenicity. Analyses were stratified according to age groups (aged 6-11 and 12-17 years).


A total of 262 participants (150 [57%] participants aged 12-17 years and 112 [43%] aged 6-11 years) were randomly assigned to receive vaccination with two doses of either ChAdOx1 nCoV-19 (n = 211 [n = 105 at day 28 and n = 106 at day 84]) or control (n = 51 [n = 26 at day 28 and n = 25 at day 84]). While solicited adverse effects were common (80% and 76% after the first and second dose, respectively), no serious adverse events related to ChAdOx1 nCoV-19 administration were recorded by the data cutoff date on October 28, 2021. Pain and tenderness were the most common local solicited adverse events. Among seronegative participants who received ChAdOx1 nCoV-19, anti-SARS-CoV-2 IgG and pseudoneutralizing antibody titers at day 28 after the second dose were higher in participants aged 12–17 years with a longer interval between doses (geometric means of 73,371 arbitrary units [AU]/mL [95% CI, 58,685–91,733] and 299 half-maximal inhibitory concentration [IC50; 95% CI, 230–390]) compared with those who received their vaccines 28 days apart (43,280 AU/mL [95% CI, 35,852–52,246] and 150 IC50 [95% CI 116–194]). Humoral responses were higher in those aged 6–11 years than in those aged 12–17 years receiving their second dose at the same 112-day interval (geometric mean ratios 1.48 [95% CI, 1.07–2.07] for anti-SARS-CoV-2 IgG and 2.96 [1.89–4.62] for pseudoneutralizing antibody titers). Cellular responses peaked after a first dose of ChAdOx1 nCoV-19 across all age and interval groups and remained above baseline after a second vaccination.


The ChAdOx1 nCoV-19 vaccine was safe, well tolerated, and immunogenic in children aged 6-17 years.


The is the first study assessing the safety and immunogenicity of the ChAdOx1 nCoV-19 vaccine in a pediatric population. While the vaccine was immunogenic, there were some differences noted, with stronger humoral immunity observed in younger (6-11 years) versus older participants (7-12 years), and in the longer dosing interval group (112 days) versus the shorter (28 days). The vaccine, however, appears to be at least as immunogenic in this population compared to adults reported in previous studies surrounding ChAdOx1 nCoV-19; implying it would confer a similar degree of protection. Whether these findings have clinical relevance is questionable given use of the ChAdOx1 nCoV-19 vaccine has been restricted due to the rare cases of thrombosis, and the BNT162b2 and mRNA-1273 are currently the most offered in high-income countries.

Clinical Topics: Congenital Heart Disease and Pediatric Cardiology, Prevention, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Prevention, CHD and Pediatrics and Quality Improvement

Keywords: Adolescent, COVID-19, COVID-19 Vaccines, Immunity, Immunogenicity, Vaccine, Outcome Assessment, Health Care, Pediatrics, Primary Prevention, SARS-CoV-2, Viral Load

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