Serosurveillance of SARS-CoV-2 in Welsh Blood Donors: Establishment of the surveillance system and results up to November 2022

BACKGROUND: In 2020, Wales experienced some of the highest rates of confirmed COVID-19 cases in Europe. We set up a serosurveillance scheme using residual samples from blood donations to inform the pandemic response in Wales. AIM: To identify changes in SARS-CoV-2 antibody seroprevalence in Wales by time, demography and location. METHODS: Residual samples from blood donations made in Wales between 29 June 2020 and 20 November 2022 were tested for antibodies to the nucleocapsid antigen (anti-N) of SARS-CoV-2, resulting from natural infection. Donations made between 12 April 2021 and 20 November 2022 were also tested for antibodies to the spike antigen (anti-S) occurring as a result of natural infection and vaccination. RESULTS: Age-standardised seroprevalence of anti-N antibodies in donors remained stable (4.4–5.5%) until November 2020 before increasing to 16.7% by February 2021. Trends remained steady until November 2021 before increasing, peaking in November 2022 (80.2%). For anti-S, seroprevalence increased from 67.1% to 98.6% between May and September 2021, then remained above 99%. Anti-N seroprevalence was highest in younger donors and in donors living in urban South Wales. In contrast, seroprevalence of anti-S was highest in older donors and was similar across regions. No significant difference was observed by sex. Seroprevalence of anti-N antibodies was higher in Black, Asian and other minority ethnicities (self-reported) compared with White donors, with the converse observed for anti-S antibodies. CONCLUSION: We successfully set up long-term serological surveillance of SARS-CoV-2 using residual samples from blood donations, demonstrating variation based on age, ethnicity and location.