Serum Samples

Random residual biochemistry serum samples (approximately 41 000) from primary (general practices) and secondary (hospitals) health care settings were collected by the NHSGGC Biorepository between the 31 March 2020 and 22 September 2021. Associated metadata included age, care type, date of sample collection, date of positive PCR result, date of first and second vaccination, and vaccine manufacturer. Seronegative samples were selected based on their enzyme-linked immunosorbent assay (ELISA) results (SARS-CoV-2 spike 1 [S1] or SARS-CoV-2 receptor-binding domain [RBD]) and the absence of a positive PCR test result or record of vaccination. Samples from vaccinated patients were selected based on their ELISA result (SARS-CoV-2 S1 or SARS-CoV-2 RBD), record of vaccination with 1 or 2 doses at least 14 days prior to blood collection, and absence of a positive PCR test result for at least 14 days after sampling. Samples from infected patients had no record of vaccination, were ELISA positive (SARS-CoV-2 S1 or SARS-CoV-2 RBD), and had a positive PCR test result at least 14 days before sample collection. Samples from infected and vaccinated patients were identified by their positive ELISA result, the presence of positive PCR test result and record of vaccination with 1 or 2 doses at least 14 days prior to blood collection. Samples from infected and infected and vaccinated patients were further stratified to infecting variants (based on the date of the positive PCR test), by identifying key time periods during which each variant was most predominant. All serum samples were inactivated at 56°C for 30 minutes before being tested.