CITF-funded scientists from Canadian Blood Services and Héma-Québec participated in an international study which looked to compare the different serological assays used across 27 countries to estimate seroprevalence. The results were recently published in Vox Sanguinis, highlighting the diversity of assays used, with the Abbott SARS-CoV-2 Ig assay being the most common.
- Seroprevalence estimates of 5.6% or less were reported in Europe, North America and Asia, whereas seroprevalence estimates of 13.5% or more were reported in Brazil and Iran. The seroprevalence rates appear to correlate with the number of COVID-19 cases in these areas.
- Several blood suppliers worldwide used the Abbott SARS-CoV-2 Ig assay.
Being able to compare seroprevalence among countries is valuable in informing policy makers, however, not every blood supplier is using the same assay to allow for this comparison. In this international study, surveys were conducted to determine the assays used, the detected immunoglobulins and target antigen, performance characteristics (sensitivity and specificity), and seroprevalence estimates in their region. Out of the suppliers contacted, 38 provided at least partial responses, representing 27 countries. Thirteen provided seroprevalence results.
The Abbott SARS-CoV-2 IgG assay was the most common kit, used by 15 blood suppliers. This was followed by the EUROIMMUN Anti-SARS-CoV-2 ELISA, and the Beijing Wantai Biological Pharmacy SARS-CoV-2 Total Ab ELISA, to name a few. Most of the assays used detect IgG, underlining the importance of IgG in immunity against SARS-CoV-2 as it declines less quickly than IgM or IgA. Of the assays, 68.2% targeted the SARS-CoV-2 spike protein and 50% targeted the nucleocapsid protein, while 18.2% targeted both viral proteins. The sensitivity of IgG-specific assays ranged from 71.9% to 100%, and the specificity ranged from 96.2% to 100%.
Among the 13 blood suppliers who provided seroprevalence estimates, 10 reported values of 5.6% or less (in Europe, North America and Asia), whereas the other four reported seroprevalence estimates of 13.5% or more (in regions of Brazil and Iran) (Table 1). The seroprevalence rates appear to correlate with the number of COVID-19 cases in these areas.
The authors highlight that it is important to consider geographic region within each country, stratification by age, and consistency in interpretation of test results when estimating seroprevalence. As there is heterogeneity in assays used, standardization of methodology is needed to allow for comparison of seroprevalence studies.
Table 1. Seroprevalence Results
|Blood component provider or country||Assay||Seroprevalence (%)||End of sampling date
|Cumulative COVID-19 incidence when sampling ended
|Canadian Blood Services (Canada)||Abbott IgG assay||0.70||2020/06/18||266|
|Héma-Québec (Québec, Canada)||In-house IgG assay||2.23||2020/07/09||660|
|American Red Cross (USA)||VITROS® Total test||1.89||2020/08/29||1811|
|Fundação Hemope (Recife, Brazil)||Abbott IgG assay||30.89||2020/07||NS|
|Fundação Pró-Sangue (São Paulo, Brazil)||Abbott IgG assay||18.33||2020/08/21||NS|
|Hemorio (Rio de Janeiro, Brazil)||MedTeste IgG/IgM (Teste Rápido)||17||2020/09||NS|
|Denmark||Zhuhai Livzon IgM/IgG Diagnostic Kit||2.00||2020/05/03||166|
|Irish Blood Transfusion Service (Ireland)||Abbott IgG assay||1.7||2020/07/16||518|
|Sanquin Blood Supply Foundation (Netherlands)||Beijing Wantai Total Ab ELISA||4.35||2020/09/02||419|
|NHS Blood and Transplant (United Kingdom)||EUROIMMUN IgG ELISA||5.6||2020/10/18||1058|
|Red Andaluza de Medicina Transfusional, Tejidos y Células (Andalusia, Spain)||Vircell ELISA IgG
Vircell ELISA IgM+IgA
IgM + IgA: 4.55
IgG and IgM + IgA: 1.03
|Japanese Red Cross Society (Japan)||Abbott IgG assay||Tokyo region: 0.4
Tohoku region: 0.2
|Iranian Blood Transfusion Organization (Iran)||Hangzhou AllTest IgG/IgM Rapid Test Dipstick (WB/S/P)||13.48||NS||130|
Both Héma-Québec and the Canadian Blood Services (CBS) collaborate with CITF to estimate seroprevalence rates for Canada and provinces served by CBS. Read more about the latest findings here.
Lewin A, Drews SJ, Lieshout‐Krikke R, Erikstrup C, Saeed S, Fady H, Uzicanin S, Custer B, O’Brien SF. An international comparison of anti‐SARS‐COV‐2 assays used for seroprevalence surveys from blood component providers. Vox Sang. 2021 Apr 29. doi: 10.1111/vox.13100.