Adolescents can develop a severe form of Coronavirus disease 2019 (COVID-19), especially with underlying comorbidities. No study has examined the efficacy or effectiveness of inactivated COVID-19 vaccines in adolescents. This single-center, prospective cohort study was performed to evaluate the safety and effectiveness of an inactivated COVID-19 vaccine in adolescents using the immunobridging approach at Chulabhorn Hospital. The key eligibility criterion was a healthy clinical condition or stable pre-existing comorbidity. The anti-receptor-binding domain (anti-RBD) antibody concentration at 4 weeks after dose 2 of the vaccine was compared between participants aged 12 to 17 years and those aged 18 to 30 years. Safety profiles included adverse events within 7 days after each dose of the vaccine and any adverse events through 1 month after dose 2 of the vaccine. In the adolescent and adult cohorts, the geometric mean concentration of anti-RBD antibody was 102.9 binding antibody unit (BAU)/mL (95% CI, 91.0–116.4) and 36.9 BAU/mL (95% CI, 30.9–44.0), respectively. The geometric mean ratio of the adolescent cohort was 2.79 (95% CI, 2.25–3.46, p < 0.0001) compared with the adult cohort, meeting the non-inferiority criterion. The reactogenicity was slightly lower in the adolescent than in the adult cohort. No serious adverse events occurred. The inactivated COVID-19 vaccine appears safe and effective in adolescents.

Coronavirus disease 2019 affected child health and impacted learning because of the resulting onsite school closures. This prospective cohort study included children aged 10–17 who received two 4 µg doses of BBIBP-CorV administered intramuscularly 21–28 days apart. To assess vaccine safety, 36,808 participants were then followed with paper- and web-based online questionnaire surveys that captured local and systemic reactogenicities following vaccine administration on days 1, 7, and 30. Among participants, 76% (27,880) reported reactogenicity within the first 24 h and 7 days following the first dose. Half (51.41%) of participants experienced pain at the injection site; the majority of cases were mild in severity. Injection site tenderness (37.93%) was another common local reaction. Fatigue (37.89%), myalgia (33.56%), and headache (26.76%) were the most common systemic reactions. On days 2–7 after the first dose, 25.85% of participants experienced adverse reactions. Following the second dose, reactogenicity was 7.6% and 1.09% within 24 h and between days 2–7. The majority of reactions were of mild to moderate severity. We report that two doses of the BBIBP-CorV caused mild to moderate side effects in adolescents in Thailand. The findings confirm the vaccine’s safety profile in this age group.

Introduction: COVID-19 pandemic affects all populations worldwide, including adolescents. Adolescents can develop a severe form of COVID-19, especially with comorbidity underlying. The prior studies of the mRNA COVID-19 vaccine showed excellent effectiveness in adolescents. Therefore, this study aimed to evaluate the safety and effectiveness of the BBIBP-CorV vaccine with the immunobridging approach in Thai adolescents. Methods: This single-center, prospective cohort study compared the immunogenicity after 2 doses of the BBIBO-CorV vaccine with 21 days interval of participants aged 12-17 years with 18-30 years at Chulabhorn Hospital, Chulabhorn Royal Academy, Bangkok, Thailand. The key eligible criteria were healthy or had stable pre-existing comorbidity participants, aged 12-17 years. The primary endpoint was the anti-receptor binding domain antibody concentration at 4 weeks after dose 2 of the vaccine. In addition, safety profiles were solicited adverse events within 7 days after each dose of vaccine and any adverse events through 1 month after dose 2 of the vaccine. Results: Four weeks after the second vaccination, the GMC of anti-RBD antibody in the adolescent cohort was 102.9 BAU/mL (95%CI; 91.0-116.4) and 36.9 BAU/mL (95%CI; 30.9-44.0) in the adult cohort. The GMR of the adolescent cohort was 2.79 (95%CI; 2.25-3.46, p-value; <0.0001) compared with the adult cohort which met non-inferiority criteria. The reactogenicity was slightly less reported in the adolescent cohort compared with the adult cohort. No serious adverse events were reported in both cohorts. Conclusion: Vaccination with the BBIBP-CorV vaccine in the adolescent participants was safe and effective.