Laboratory testing
Blood was collected from all participants at enrolment, and serum was
stored at -20°C until testing. Sera samples were tested for anti-spike
antibodies with Wantai SARS-CoV-2 total antibody ELISA (Beijing Wantai
Biological Pharmacy, Beijing, China) and for anti-nucleocapsid
antibodies using Platelia SARS-CoV-2 total antibody ELISA (Bio-Rad
Laboratories, Hercules, CA) in the InterDiagnostic Clinic Laboratory,
Baku. The manufacturer’s recommended controls and thresholds were used
to define seropositivity. For participants who had haemolysed or
insufficient specimens, repeat blood draws were performed within 30 days
of enrolment.
A subset of SARS-CoV-2 PCR-positive study samples was sent to the
Charite University Institute of Virology laboratory in Berlin, Germany,
for whole genome sequencing (WGS).