Serosurveillance for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Incidence Using Global Blood Donor Populations

Association between ABO blood groups and SARS-CoV-2 infection in blood donors of Puglia region

This is an observational multicentric cross-sectional study aiming at assessing the association between ABO blood groups and SARS-CoV-2 seroprevalence among the blood donors in Puglia region. Data on ABO and Rh blood groups and demographic characteristics were obtained from Blood Bank Information System. All donors were screened for SARS-CoV-2 IgG antibodies. Comparison of seroprevalence among blood groups and the association between the recorded variables and seroprevalence were evaluated. A total of 35,709 donors from 22 centers were included, with a seroprevalence of 6.8%. The distribution of ABO phenotypes was blood type O (46.8%), A (34.0%), B (14.7%), and AB (4.5%). Among the 2416 donors reactive for SARS-CoV-2 IgG, the prevalent phenotype was blood type O (43.1%), followed by A (37.7%), B (14.2%), and AB (5%). The seroprevalence of phenotype A and AB was 7.5%, followed by B (6.5%) and O (6.2%). According to the adjusted analysis, there was an increase in seroprevalence in groups A and AB, compared to group O, and an increase in males compared to females. A possible effect modification was observed after stratifying for sex (p = 0.0515). A significantly lower prevalence of blood type O was found compared to A and AB, whereas no association was observed between Rh factor and seroprevalence. We hypothesized that the A antigen present in blood type A and AB can play a role in the binding of SARS-CoV-2 to ACE2 receptors, resulting in an increased risk of infection. Furthermore, natural anti-A/anti-B antibodies produced in group O could block viral adhesion to cells and explain a lower risk of infection.

Seroprevalence of SARS-CoV-2 anti-nucleocapsid total Ig, anti-RBD IgG antibodies, and infection in Thailand: a cross-sectional survey from October 2022 to January 2023

Seroprevalence studies on SARS-CoV-2 are essential for estimating actual prevalence rates of infection and vaccination in communities. This study evaluated infection rates based on total anti-nucleocapsid immunoglobulin (N) and/or infection history. We determined the seroprevalence of anti-receptor binding domain (RBD) antibodies across age groups. A cross-sectional study was conducted in Chonburi province, Thailand, between October 2022 and January 2023. Participants included newborns to adults aged up to 80 years. All serum samples were tested for anti-N total Ig and anti-RBD IgG. The interviewer-administered questionnaires queried information on infection history and vaccination records. Of 1459 participants enrolled from the Chonburi population, ~ 72.4% were infected. The number of infections was higher in children aged < 5 years, with evidence of SARS-CoV-2 infection decreasing significantly with increasing age. There were no significant differences based on sex or occupation. Overall, ~ 97.4% of participants had an immune response against SARS-CoV-2. The anti-RBD IgG seroprevalence rate was lower in younger vaccinated individuals and was slightly increased to 100% seropositivity at ages > 60 years. Our findings will help predict the exact number of infections and the seroprevalence of SARS-CoV-2 in the Thai population. Furthermore, this information is essential for public health decision-making and the development of vaccination strategies.

Cohort profile: a longitudinal regional cohort study to assess COVID-19 seroprevalence in blood donors - baseline characteristics of the SeMaCo study participants

PURPOSE

The SeMaCo study (Serologische Untersuchungen bei Blutspendern des Großraums Magdeburg auf Antikörper gegen SARS-CoV-2), a prospective, longitudinal cohort study with four survey phases spanning 3-5 months each over a period of 22 months, extends the spectrum of seroepidemiological studies in Germany. We present here a careful characterisation of the initial survey phase of the cohort to provide baseline data on infection incidence and obtained from questionnaires, focussing in particular on the attitude towards COVID-19 vaccinations, the vaccination success and the vaccination acceptance.

PARTICIPANTS

A total of 2195 individual blood donors from the donor pool of the blood donation service of the University Hospital Magdeburg were enrolled in the initial survey phase from 20 January 2021 to 30 April 2021. 2138 participants gave sociodemographic/contact data (51.7% male, mean age 44 years) and 2082 participants answered the vaccination questionnaire.

FINDINGS TO DATE

Out of 2195 participants with antibody results, 1909 (87.0%) were antibody negative. The remaining 286 subjects (13.0%) were either antibody-positive and vaccinated (160/286; 55.9%) or antibody-positive without vaccination information (17/286; 5.9%) or antibody-positive and unvaccinated (109/286; 38.1%). The latter result reflects the rate of true or highly probable SARS-CoV-2 infections in our initial study cohort.

FUTURE PLANS

The study primarily aims to measure the prevalence and long-term kinetics of IgG-antibodies against SARS-CoV-2. Including the baseline, the study foresees four survey periods of 3-4 months each. At each visit, we will assess the blood donors' attitude towards vaccination, the antibody response following vaccination and/or infection, as well as undesired vaccination effects. We aim to test the same participants during the survey periods by repeated invitations for blood donation to ensure a long-term (follow-up) in as many study participants as possible. After the four survey phases, a longitudinal data set will be created that reflects the course of the antibody levels/frequencies as well as the infection and vaccination incidence.

TRIAL REGISTRATION NUMBER

DRKS00023263.

Cross-Canada Variability in Blood Donor SARS-CoV-2 Seroprevalence by Social Determinants of Health

We compared the seroprevalence of SARS-CoV-2 anti-nucleocapsid antibodies in blood donors across Canadian regions in 2021. The seroprevalence was the highest in Alberta and the Prairies, and it was so low in Atlantic Canada that few correlates were observed. Being male and of young age were predictive of seropositivity. Racialization was associated with higher seroprevalence in British Columbia and Ontario but not in Alberta and the Prairies. Living in a materially deprived neighborhood predicted higher seroprevalence, but it was more linear across quintiles in Alberta and the Prairies, whereas in British Columbia and Ontario, the most affluent 60% were similarly low and the most deprived 40% similarly elevated. Living in a more socially deprived neighborhood (more single individuals and one parent families) was associated with lower seroprevalence in British Columbia and Ontario but not in Alberta and the Prairies. These data show striking variability in SARS-CoV-2 seroprevalence across regions by social determinants of health. IMPORTANCE Canadian blood donors are a healthy adult population that shows clear disparities associated with racialization and material deprivation. This underscores the pervasiveness of the socioeconomic gradient on SARS-CoV-2 infections in Canada. We identify regional differences in the relationship between SARS-CoV-2 seroprevalence and social determinants of health. Cross-Canada studies, such as ours, are rare because health information is under provincial jurisdiction and is not available in sufficient detail in national data sets, whereas other national seroprevalence studies have insufficient sample sizes for regional comparisons. Ours is the largest seroprevalence study in Canada. An important strength of our study is the interpretation input from a public health team that represented multiple Canadian provinces. Our blood donor seroprevalence study has informed Canadian public health policy at national and provincial levels since the start of the SARS-CoV-2 pandemic.

Anti-SARS-CoV-2 antibody among SARS-CoV-2 vaccinated vs post-infected blood donors in a tertiary hospital, Bangkok, Thailand

SARS-CoV-2 virus infection has imposed a significant healthcare burden globally. To contain its spread and decrease infection-related mortality, several vaccines have been deployed worldwide in the past 3 years. We conducted a cross-sectional seroprevalence study to assess the immune response against the virus among blood donors at a tertiary care hospital, Bangkok, Thailand. From December 2021 to March 2022, total of 1,520 participants were enrolled, and their past history of SARS-CoV-2 infection and vaccination was recorded. Two serology test, namely, quantitative IgG spike protein (IgGSP) and qualitative IgG nucleocapsid antibody (IgGNC) were performed. The median age of study participants was 40 years (IQR 30-48) and 833 (54.8%) were men. Vaccine uptake was reported in 1,500 donors (98.7%) and 84 (5.5%) reported the past infection history. IgGNC was detected in 46/84 donors with the past infection history (54.8%) and in 36 out of the rest 1,436 (2.5%) with no past history. IgGSP positivity was observed in 1484 donors (97.6%). When compared to unvaccinated donors (n = 20), IgGSP level was higher in the donors who had received one vaccine dose (p< 0.001) and these antibody levels increased significantly among those with 3rd and 4th vaccine doses. Factors associated with low IgGSP (lowest quartile) by multivariate analysis included: no past infection history, homologous vaccination, < 3 vaccine doses, and > 90 days duration since last vaccination. In conclusion, vaccine uptake among our study donors was high (98.7%) and IgGSP antibody was observed in nearly all the vaccinated donors (97.6%). Previous SARS-CoV-2 infection, use of heterologous vaccination, vaccines ≥ 3 doses, and duration of the last vaccination >90 days affected IgGSP levels. Use of serological assays were found beneficial in the evaluation and differentiation of immune response to vaccination, and natural infection including the identification of previous asymptomatic infections.

SARS-CoV-2 Seroprevalence among Canadian Blood Donors: The Advance of Omicron

With the emergence of the SARS-CoV-2 Omicron variant in late 2021, Canadian public health case/contact testing was scaled back due to high infection rates with milder symptoms in a highly vaccinated population. We monitored the seroprevalence of SARS-CoV-2 nucleocapsid (anti-N) and spike protein (anti-S) antibodies in blood donors across Canada from September 2021 to June 2022 in 202,123 randomly selected samples. Multivariable logistic regression of anti-N positivity with month, age, sex, racialization, region, material and social deprivation (based on postal code) identified as independent predictors. Piece-wise logistic regression analysed the association between anti-S concentration and month, and anti-N/anti-S positivity. Infection-related seroprevalence (anti-N positive) was 4.38% (95% CI: 3.96, 4.81) in September reaching 50.70% (50.15, 52.16) in June; nearly 100% were anti-S positive throughout. Anti-N positivity was associated with younger age, male sex, the Alberta and Prairies regions, greater material deprivation and less social deprivation (p < 0.001). Anti-S concentration was high initially (3306 U/mL, IQR 4280 U/mL), increased to (13,659 U/mL, IQR 28,224 U/mL) by June (p < 0.001), following the pattern of deployment of the third and fourth vaccine doses and was higher in those that were anti-N positive (p < 0.001). Despite already high vaccination-related seroprevalence, infection-related seroprevalence increased dramatically with the emergence of the Omicron SARS-CoV-2 variant.

SARS-CoV-2 Seroepidemiological Investigation in Jordan: Seroprevalence, Herd Immunity, and Vaccination Coverage. A Population-Based National Study

Background

Population-based serosurveillance is a cornerstone to furthering our understanding of the COVID-19 pandemic at the community levels. In Jordan, four waves (phases) of seroprevalence epidemiological investigations were conducted using representative population-based national samples. This study aims to estimate the population-based seropositivity, herd immunity, and vaccination coverage at the fourth wave.

Methods

Multistage sampling technique was implemented to recruit a nationally representative sample for the fourth wave of the seroprevalence investigation (June to August 2021). Electronically collected data utilized a questionnaire on background demographics, chronic diseases, and COVID-19 vaccination history. Also, blood samples were collected to detect the presence of total Anti-SARS-CoV-2 IgM and IgG using Wantai/ELISA assays. Prevalence estimates were presented using percentage and 95% Confidence Intervals (C.I.).

Results

There were 8821 participants included in this study, with a mean age of 31.3 years, and 61.7% were females. COVID-19 national seroprevalence and vaccination coverage estimates were 74.1% (95% C.I.: 73.1–74.9%) and 38.4% (95% C.I.: 37.1–39.6%), respectively. Among children, seroprevalence estimates were similar to unvaccinated adults. Among COVID-19 adults, 57.2% were vaccinated. Among vaccinated participants, 91.5% were seropositive, while among unvaccinated, 63.2% were seropositive. By age group, seroprevalence ranged between 53.0% and 86.9%. Seroprevalence estimates were significantly different by gender, vaccination status and dose, and residence.

Conclusion

The reported interplay between seropositivity and vaccination coverage estimate seems insufficient to provide herd immunity levels to combat new variants of SARS-CoV-2. Children and healthcare workers seem to be an epidemiologically influential group in spreading COVID-19. As the globe is still grappling with SARS-CoV-2 infection, national seroepidemiological evidence from Jordan calls for more focus on vaccination coverage, especially among epidemiologically vulnerable groups, to optimize herd immunity.

Seroprevalence of SARS-CoV-2 Antibodies among Vaccinated and Non-Vaccinated Adults in the West Bank: Results of a Repeated Cross-Sectional Study

Seroprevalence studies provide an accurate measure of SARS-CoV-2 spread at a population level and the number of undiagnosed individuals. Repeated cross-sectional sero-studies are encouraged to monitor the spread of the virus. The aim of this study is to assess the seroprevalence rate among a random sample of Palestinians residing in the West Bank region of Palestine, especially among those who were not vaccinated and not diagnosed. The study was able to assess the prevalence of asymptomatic cases among the Palestinian adult population. The study also focused on measuring the percentage of adult Palestinians who accepted to get vaccinated across gender and age groups. Methods: This second round cross-sectional study involved 1451 participants, who agreed to be interviewed and answer the questionnaire, where 910 of them agreed to participate in the sero-study and donate a blood sample to be tested for antibodies. The sample was randomly selected from the adult population, 18 years or older, living in the West Bank region of Palestine. Serological tests for 910 adequate serum samples were performed using immunoassays for the detection of antibodies against SARS-CoV-2. Sociodemographic information and medical history data were collected. Results: Study findings indicate that as of October 2021, there was a seroprevalence rate of 75.9% (30% due to infection with COVID-19 virus and 45.9% due to vaccination) with 95% CI (73.1−78.7). The results indicate that the prevalence of antibodies among those who are unvaccinated and undiagnosed was 45.2% with 95% CI (39.9−50.5%). The average age of participants was 37.6 years old. A total of 49.2% were females, and 50.8% were males. In relation to COVID-19, 13.6% of respondents reported getting infected by COVID-19 with statistically significant difference (p-value = 0.001) between males (10.7%) and females (16.5%). In terms of vaccination, 52.8% of respondents reported getting vaccinated with an important difference between males (64.3%) and females (40.9%), (p-value < 0.01). Conclusions: Our findings reveal a drastic rise in seroprevalence of SARS-CoV-2 antibodies due to infection and vaccination. This information is useful for assessing the degree of herd immunity among the adult population and provides better understanding of the pandemic. Population-based seroprevalence studies should be conducted periodically to monitor the SARS-CoV-2 seroprevalence in Palestine and inform policy makers about the efficacy of the surveillance system and the public compliance with vaccination policies especially among females.

Association of Trends in Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Seroprevalence and State-Issued Nonpharmaceutical Interventions: United States, 1 August 2020 to 30 March 2021

BACKGROUND

We assess if state-issued nonpharmaceutical interventions (NPIs) are associated with reduced rates of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection as measured through anti-nucleocapsid (anti-N) seroprevalence, a proxy for cumulative prior infection that distinguishes seropositivity from vaccination.

METHODS

Monthly anti-N seroprevalence during 1 August 2020 to 30 March 2021 was estimated using a nationwide blood donor serosurvey. Using multivariable logistic regression models, we measured the association of seropositivity and state-issued, county-specific NPIs for mask mandates, gathering bans, and bar closures.

RESULTS

Compared with individuals living in a county with all three NPIs in place, the odds of having anti-N antibodies were 2.2 (95% confidence interval [CI]: 2.0-2.3) times higher for people living in a county that did not have any of the 3 NPIs, 1.6 (95% CI: 1.5-1.7) times higher for people living in a county that only had a mask mandate and gathering ban policy, and 1.4 (95% CI: 1.3-1.5) times higher for people living in a county that had only a mask mandate.

CONCLUSIONS

Consistent with studies assessing NPIs relative to COVID-19 incidence and mortality, the presence of NPIs were associated with lower SARS-CoV-2 seroprevalence indicating lower rates of cumulative infections. Multiple NPIs are likely more effective than single NPIs.

Serosurvey for SARS-CoV-2 among blood donors in Wuhan, China from September to December 2019

The emerging of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused COVID-19 pandemic. The first case of COVID-19 was reported at early December in 2019 in Wuhan City, China. To examine specific antibodies against SARS-CoV-2 in biological samples before December 2019 would give clues when the epidemic of SARS-CoV-2 might start to circulate in populations. We obtained all 88,517 plasmas from 76,844 blood donors in Wuhan between 1 September and 31 December 2019. We first evaluated the pan-immunoglobin (pan-Ig) against SARS-CoV-2 in 43,850 samples from 32,484 blood donors with suitable sample quality and enough volume. Two hundred and sixty-four samples from 213 donors were pan-Ig reactive, then further tested IgG and IgM, and validated by neutralizing antibodies against SARS-CoV-2. Two hundred and thirteen samples (from 175 donors) were only pan-Ig reactive, 8 (from 4 donors) were pan-Ig and IgG reactive, and 43 (from 34 donors) were pan-Ig and IgM reactive. Microneutralization assay showed all negative results. In addition, 213 screened reactive donors were analyzed and did not show obviously temporal or regional tendency, but the distribution of age showed a difference compared with all tested donors. Then we reviewed SARS-CoV-2 antibody results from these donors who donated several times from September 2019 to June 2020, partly tested in a previous published study, no one was found a significant increase in S/CO of antibodies against SARS-CoV-2. Our findings showed no SARS-CoV-2-specific antibodies existing among blood donors in Wuhan, China before 2020, indicating no evidence of transmission of COVID-19 before December 2019 in Wuhan, China.

Changing Patterns of SARS-CoV-2 Seroprevalence among Canadian Blood Donors during the Vaccine Era

We monitored the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (anti-N; proxy of natural infection) and spike protein (anti-S; proxy for humoral immunity) antibodies in blood donors across Canada from January to November 2021. The first and second doses of vaccine were deployed over this time. Anti-N seroprevalence remained low overall (about 5% or lower) from January to November but was higher in racialized groups, younger age groups, and those living in materially deprived neighborhoods. Anti-S seroprevalence corresponded with the roll out of vaccines across the country, increasing in April in older donors and then progressively to younger age groups consistent with vaccination policies targeting oldest to youngest. By November, close to 100% of blood donors were positive for anti-S. Anti-S concentrations peaked by July and began waning by September to November particularly in older donors. These data have informed national and provincial public health policy in Canada throughout vaccination rollout.

IMPORTANCE Throughout the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, our blood donor seroprevalence study has informed Canadian public health policy at national and provincial levels. We describe the only continuously running national seroprevalence study in Canada, which spans the full length of the pandemic and per capita is one of the largest programs in the world. The benefit of seroprevalence studies is that they identify a broad range of asymptomatic and symptomatic infection histories that may not be identified with active SARS-CoV-2 nucleic acid testing programs or when case definitions change. As vaccination was deployed in Canada, we estimated the proportion of donors with vaccine-related antibodies and developed population-level estimates of SARS-CoV-2 spike antibody concentrations. Monthly predictive mathematical models and our results engaged public health organizations in new ways. In the future, we intend to continue to expand on these interactions with provincial and national public health teams.

Persistence of SARS-CoV-2 total immunoglobulins in a series of convalescent plasma and blood donors

Background

The vast majority of COVID-19 cases both symptomatic and asymptomatic develop immunity after COVID-19 contagion. Whether lasting differences exist between infection and vaccination boosted immunity is yet to be known. The aim of this study was to determine how long total anti-SARS-CoV2 antibodies due to past infection persist in peripheral blood and whether sex, age or haematological features can influence their lasting.

Material and methods

A series of 2421 donations either of SARS-CoV-2 convalescent plasma or whole blood from 1107 repeat donors from January 2020 to March 2021 was analysed. An automated chemiluminescence immunoassay for total antibodies recognizing the nucleocapsid protein of SARS-CoV-2 in human serum and plasma was performed. Sex, age, blood group, blood cell counts and percentages and immunoglobulin concentrations were extracted from electronic recordings. Blood donation is allowed after a minimum of one-month post symptom’s relapse. Donors were 69.7% males and their average age was 46. The 250 donors who had later donations after a positive one underwent further analysis. Both qualitative (positivity) and quantitative (rise or decline of optical density regarding consecutive donations) outcomes were evaluated.

Results and discussion

In 97.6% of donors with follow-up, anti-SARS-CoV-2 protein N total antibodies remained positive at the end of a follow-up period of 12.4 weeks median time (1–46, SD = 9.65) after the first positive determination. The blood group was not related to antibody waning. Lower lymphocyte counts and higher neutrophils would help predict future waning or decay of antibodies. Most recovered donors maintain their total anti-SARS-CoV-2 N protein antibodies for at least 16 weeks (at least one month must have been awaited from infection resolution to blood donation). The 10 individuals that could be followed up longer than 40 weeks (approximately 44 weeks after symptom’s relapse) were all still positive.

SARS-CoV-2 IgG Seroprevalence among Blood Donors as a Monitor of the COVID-19 Epidemic, Brazil

During epidemics, data from different sources can provide information on varying aspects of the epidemic process. Serology-based epidemiologic surveys could be used to compose a consistent epidemic scenario. We assessed the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG in serum samples collected from 7,837 blood donors in 7 cities of Brazil during March–December 2020. Based on our results, we propose a modification in a compartmental model that uses reported number of SARS-CoV-2 cases and serology results from blood donors as inputs and delivers estimates of hidden variables, such as daily values of SARS-CoV-2 transmission rates and cumulative incidence rate of reported and unreported SARS-CoV-2 cases. We concluded that the information about cumulative incidence of a disease in a city’s population can be obtained by testing serum samples collected from blood donors. Our proposed method also can be extended to surveillance of other infectious diseases.

Public health impact of the Pfizer-BioNTech COVID-19 vaccine (BNT162b2) in the first year of rollout in the United States

BACKGROUND

As the body of evidence on COVID-19 and post-vaccination outcomes continues to expand, this analysis sought to evaluate the public health impact of the Pfizer-BioNTech COVID-19 Vaccine, BNT162b2, during the first year of its rollout in the US.

METHODS

A combined Markov decision tree model compared clinical and economic outcomes of the Pfizer-BioNTech COVID-19 Vaccine (BNT162b2) versus no vaccination in individuals aged ≥12 years. Age-stratified epidemiological, clinical, economic, and humanistic parameters were derived from existing data and published literature. Scenario analysis explored the impact of using lower and upper bounds of parameters on the results. The health benefits were estimated as the number of COVID-19 symptomatic cases, hospitalizations and deaths averted, and Quality Adjusted Life Years (QALYs) saved. The economic benefits were estimated as the amount of healthcare and societal cost savings associated with the vaccine-preventable health outcomes.

RESULTS

It was estimated that, in 2021, the Pfizer-BioNTech COVID-19 Vaccine (BNT162b2) contributed to averting almost 9 million symptomatic cases, close to 700,000 hospitalizations, and over 110,000 deaths, resulting in an estimated $30.4 billion direct healthcare cost savings, $43.7 billion indirect cost savings related to productivity loss, as well as discounted gains of 1.1 million QALYs. Scenario analyses showed that these results were robust; the use of alternative plausible ranges of parameters did not change the interpretation of the findings.

CONCLUSIONS

The Pfizer-BioNTech COVID-19 Vaccine (BNT162b2) contributed to generate substantial public health impact and vaccine-preventable cost savings in the first year of its rollout in the US. The vaccine was estimated to prevent millions of COVID-19 symptomatic cases and thousands of hospitalizations and deaths, and these averted outcomes translated into cost-savings in the billions of US dollars and thousands of QALYs saved. As only direct impacts of vaccination were considered, these estimates may be conservative.

Current challenges of severe acute respiratory syndrome coronavirus 2 seroprevalence studies among blood donors: A scoping review

BACKGROUND AND OBJECTIVES

Blood donors are increasingly being recognized as an informative resource for surveillance. We aimed to review severe acute respiratory syndrome coronavirus 2 seroprevalence studies conducted among blood donors to investigate methodological biases and provide guidance for future research.

MATERIALS AND METHODS

We conducted a scoping review of peer-reviewed and preprint publications between January 2020 and January 2021. Two reviewers used standardized forms to extract seroprevalence estimates and data on methodology pertaining to population sampling, periodicity, assay characteristics, and antibody kinetics. National data on cumulative incidence and social distancing policies were extracted from publicly available sources and summarized.

RESULTS

Thirty-three studies representing 1,323,307 blood donations from 20 countries worldwide were included (sample sizes ranged from 22 to 953,926 donations). The majority of the studies (79%) reported seroprevalence rates <10% (ranging from 0% to 76% [after adjusting for waning antibodies]). Overall, less than 1 in 5 studies reported standardized seroprevalence rates to reflect the demographics of the general population. Stratification by age and sex were most common (64% of studies), followed by region (48%). A total of 52% of studies reported seroprevalence at a single time point. Overall, 27 unique assay combinations were identified, 55% of studies used a single assay and only 39% adjusted seroprevalence rates for imperfect test characteristics. Among the nationally representative studies, case detection was most underrepresented in Kenya (1:1264).

CONCLUSION

By the end of 2020, seroprevalence rates were far from reaching herd immunity. In addition to differences in community transmission and diverse public health policies, study designs and methodology were likely contributing factors to seroprevalence heterogeneity.

Increased SARS-CoV-2 seroprevalence in healthy blood donors after the second pandemic wave in South-Eastern Italy: evidence for asymptomatic young donors as potential virus spreaders

BACKGROUND

Italy experienced SARS-CoV-2 spread during the second wave and the southern regions were severely affected. In this prospective study, we assessed the changes in SARS-CoV-2 seroprevalence rates in non-vaccinated blood donors to evaluate the spread of SARS-CoV-2 among healthy individuals in our geographical area.

METHODS

8,183 healthy blood donors visiting the Transfusion Centre at the University Hospital "Riuniti" of Foggia (Italy) to donate blood from May 2020 to March 2021 were tested twice for anti-SARS-CoV-2 antibodies by Ortho Clinical Diagnostics VITROS^® 3600 through anti-SARS-CoV-2 Total and IgG reagent kit. None of the subjects had diagnosed symptomatic COVID-19 infection, and none had received vaccination.

RESULTS

Overall, 516 out of 8,183 had antibodies to SARS-CoV-2 (total and IgG antibodies) (6.3%, 95% CI: 0.03-0.15%), 387 were male and 129 female. There was a significant increase of seropositive donors from May 2020 to March 2021 (p < .001). The difference in seroprevalence was significantly associated with age but not sex (2-sided p < .05 for age; 2-sided p ≥ .05 for sex) in both groups.

CONCLUSIONS

Our study showed a significant increase in SARS-CoV-2 seroprevalence in blood donors and suggests that asymptomatic individuals might contribute to the spread of SARS-CoV-2. These results may contribute to revised containment measures, priorities in vaccine campaigns and monitoring of seroprevalence in public places like Transfusion Centres. Serologic testing of blood donors may be relevant to monitor SARS-CoV-2 circulation in the general population.

Estimated US Infection- and Vaccine-Induced SARS-CoV-2 Seroprevalence Based on Blood Donations, July 2020-May 2021

IMPORTANCE

People who have been infected with or vaccinated against SARS-CoV-2 have reduced risk of subsequent infection, but the proportion of people in the US with SARS-CoV-2 antibodies from infection or vaccination is uncertain.

OBJECTIVE

To estimate trends in SARS-CoV-2 seroprevalence related to infection and vaccination in the US population.

DESIGN, SETTING, AND PARTICIPANTS

In a repeated cross-sectional study conducted each month during July 2020 through May 2021, 17 blood collection organizations with blood donations from all 50 US states; Washington, DC; and Puerto Rico were organized into 66 study-specific regions, representing a catchment of 74% of the US population. For each study region, specimens from a median of approximately 2000 blood donors were selected and tested each month; a total of 1 594 363 specimens were initially selected and tested. The final date of blood donation collection was May 31, 2021.

EXPOSURE

Calendar time.

MAIN OUTCOMES AND MEASURES

Proportion of persons with detectable SARS-CoV-2 spike and nucleocapsid antibodies. Seroprevalence was weighted for demographic differences between the blood donor sample and general population. Infection-induced seroprevalence was defined as the prevalence of the population with both spike and nucleocapsid antibodies. Combined infection- and vaccination-induced seroprevalence was defined as the prevalence of the population with spike antibodies. The seroprevalence estimates were compared with cumulative COVID-19 case report incidence rates.

RESULTS

Among 1 443 519 specimens included, 733 052 (50.8%) were from women, 174 842 (12.1%) were from persons aged 16 to 29 years, 292 258 (20.2%) were from persons aged 65 years and older, 36 654 (2.5%) were from non-Hispanic Black persons, and 88 773 (6.1%) were from Hispanic persons. The overall infection-induced SARS-CoV-2 seroprevalence estimate increased from 3.5% (95% CI, 3.2%-3.8%) in July 2020 to 20.2% (95% CI, 19.9%-20.6%) in May 2021; the combined infection- and vaccination-induced seroprevalence estimate in May 2021 was 83.3% (95% CI, 82.9%-83.7%). By May 2021, 2.1 SARS-CoV-2 infections (95% CI, 2.0-2.1) per reported COVID-19 case were estimated to have occurred.

CONCLUSIONS AND RELEVANCE

Based on a sample of blood donations in the US from July 2020 through May 2021, vaccine- and infection-induced SARS-CoV-2 seroprevalence increased over time and varied by age, race and ethnicity, and geographic region. Despite weighting to adjust for demographic differences, these findings from a national sample of blood donors may not be representative of the entire US population.

Dramatic rise in seroprevalence rates of SARS-CoV-2 antibodies among healthy blood donors: The evolution of a pandemic

BACKGROUND

Seroprevalence studies of SARS-CoV-2 antibodies are useful in assessing the epidemiological status in the community, and the degree of spread.

OBJECTIVE

To study the seroprevalence rates of SARS-CoV-2 antibodies among healthy blood donors in Jordan, at various points of time and as the pandemic evolves in the community.

METHODS

In total, 1374 blood donor samples, from three groups, were tested for SARS-CoV-2 total immunoglobulin antibodies. In the first group, samples from 734 individuals (from donations made between January and June 2020) were tested in June. In the second group, 348 individuals were tested in September 2020. The third group of 292 individuals was tested in February 2021. A qualitative assay was used for testing (specificity 99.8%, sensitivity 100%).

RESULTS

The first two groups, from January-June and September 2020, when confirmed Covid-19 cases numbered between several hundred and 3000, showed a seroprevalence rate of 0% (95% CI 0.00-0.51%). The third group (early February 2021), when the number of confirmed cases had reached 100 times that of September 2020, revealed a seroprevalence of 27.4% (95% CI 22.5-32.9%).

CONCLUSIONS

A dramatic rise in seroprevalence of SARS-CoV-2 antibodies was seen among healthy blood donors in Jordan, in parallel with widespread intracommunity transmission of the disease. This information is useful for assessing the degree of herd immunity, and provides for better understanding of the pandemic.

We stand ready … Blood collection organizations and the COVID-19 pandemic

See article on page 1471–1478, in this issue

Dramatic rise in seroprevalence rates of SARS-CoV-2 antibodies among healthy blood donors: The evolution of a pandemic

BACKGROUND

Seroprevalence studies of SARS-CoV-2 antibodies are useful in assessing the epidemiological status in the community, and the degree of spread.

OBJECTIVE

To study the seroprevalence rates of SARS-CoV-2 antibodies among healthy blood donors in Jordan, at various points of time and as the pandemic evolves in the community.

METHODS

In total, 1374 blood donor samples, from three groups, were tested for SARS-CoV-2 total immunoglobulin antibodies. In the first group, samples from 734 individuals (from donations made between January and June 2020) were tested in June. In the second group, 348 individuals were tested in September 2020. The third group of 292 individuals was tested in February 2021. A qualitative assay was used for testing (specificity 99.8%, sensitivity 100%).

RESULTS

The first two groups, from January-June and September 2020, when confirmed Covid-19 cases numbered between several hundred and 3000, showed a seroprevalence rate of 0% (95% CI 0.00-0.51%). The third group (early February 2021), when the number of confirmed cases had reached 100 times that of September 2020, revealed a seroprevalence of 27.4% (95% CI 22.5-32.9%).

CONCLUSIONS

A dramatic rise in seroprevalence of SARS-CoV-2 antibodies was seen among healthy blood donors in Jordan, in parallel with widespread intracommunity transmission of the disease. This information is useful for assessing the degree of herd immunity, and provides for better understanding of the pandemic.