Subject recruitment
Children and adolescents under 18 years of age who had recovered from
COVID-19 were recruited to the study. These subjects were admitted and
managed in the Paediatric Infectious Disease Centre, Princess Margaret
Hospital, Hong Kong, China. Patients were confirmed to have COVID-19 by
a positive SARS-CoV-2 RT-PCR test of their nasopharyngeal swab(NPS).
Patients were confirmed to have recovered from COVID-19 by either two
consecutives negative NPS by SARS-CoV-2 RT-PCR or the seroconversion of
SARS-CoV-2 anti-NP antibody response. Details of the admission and
discharge criteria and the laboratory investigations have been
previously described.[23] Their demographics, clinical symptoms
during the infection, and time since recovery were retrieved.
Uninfected controls were recruited from pediatric patients admitted to
the Queen Mary Hospital for follow up of other medical conditions
unrelated to COVID-19 or from healthy individuals in the community
(Table S1). Subjects below 18 years of age with no history of COVID-19
and a negative SARS-CoV-2 RT-PCR on the day of recruitment were invited
to participate in the study. Exclusion criteria included participants
with other acute infections 2 weeks before recruitment, having received
any kinds of COVID-19 vaccines, known underlying primary or acquired
immunodeficiency, and autoimmune disease or other condition that
required immunosuppressants.