The COVID-19 pandemic has caused more than 100 million cases and 3 million deaths globally, and over 10,000 cases in Hong Kong. The virus may cause long COVID and multisystem inflammatory syndrome in children. Some emerging virus variants have also been found to be more infectious to teenagers. Children and adolescents under 20 years old are contagious, and infected children may spread the virus to their grandparents. The prolonged suspension of classes and social distancing have also had a negative impact on students. Therefore, children and adolescents urgently need to be immunised against COVID-19. The Department of Paediatrics and Adolescent Medicine and School of Public Health at HKUMed launched the COVID-19 Vaccination in Adolescents (COVA) study. Timely local data on the reactogenicity and immunogenicity of COVID-19 vaccines in adolescents inform the public and the government whether the vaccines should be given to adolescents, and allow complete school reopening as soon as possible. This study has been approved by the Institutional Review Board of HKU/Hospital Authority HK West Cluster.