Evaluate the Safety and Immunogenicity of Ad5 COVID-19 Vaccines for Booster Use in Children Aged 6-17 Years.

Participants will be randomized into two age groups: children aged 6-12 years and adolescents aged 13-17 years. Subjects who have previously been immunized with 2 doses of inactivated COVID-19 vaccine will be randomized into the booster dose groups to receive either 1 dose of 0.1ml inhaled Ad5- nCoV-IH, 1 dose of 0.3ml intramuscular Ad5-nCoV-IM or 1 dose of 0.5ml intramuscular inactivated vaccine ICV as activecomparator in a ratio of 3:1:1. Participants who have not received any COVID-19 vaccine previously will be randomized into 2 primary dose age groups: children aged 6-12 years and adolescents aged 13-17 years to receive 2 doses of 0.1ml inhaled Ad5-nCoVIH. The first 5 subjects of each age group will enter the sentinel group to receive Ad5-nCoV-IH and monitor for safety before the rest of the enrollment process.