COVID-19 Seroprevalence Test for IgG Antibody Levels Among Healthy Donors Across Different Pandemic Phases in Jeddah
June 24th, 2025
This study assessed COVID-19 seroprevalence in Jeddah, Saudi Arabia, among healthy blood donors across pre-lockdown, during-lockdown, and post-lockdown periods. Of 3,825 samples, 4.5% tested positive for IgG antibodies. Seroprevalence increased significantly post-lockdown, highlighting the role of asymptomatic transmission and the effectiveness of initial restrictions.
This research examined the IgG seroprevalence in healthy Jeddah donors across the early COVID-19 pandemic to assessing the immunity after, during, and before lockdown. Our research uses ELISA, PCR, and high-throughput serology platform and statistical modelings tool to measure antibody level and in the medium. To begin, obtain blood samples from healthy patients who do not have any history of COVID-19.
Centrifuge the samples at 200 G for 10 minutes to obtain the serum supernatant. Store at minus 20 degrees Celsius in a biosafety level three facility at the SIAU until testing. To screen for anti-SARS-CoV-2 IgG antibodies, coat microtiter plates with 100 nanograms of SARS-CoV-2 spike recombinant protein diluted in PBS.
Incubate the plates overnight at four degrees Celsius. Wash the plates three times with PBST, then add 5%skim milk to block the plates and incubate. Wash the plates three more times with PBST after blocking.
Now, dilute the sera samples at a ratio of one to 100 in 5%skim milk. Add 100 microliters of diluted sera into each well. Then, incubate the plate at 37 degrees Celsius for one hour.
After washing the plates three more times with PBST, pipette each well with 100 microliters of goat KPL peroxidase-labeled antibodies to human IgG. Incubate the plate for one hour at 37 degrees Celsius before washing the plates with PBST. Next, pipette 100 microliters of TMB to each well.
Incubate for five minutes for color development. Stop the reaction by adding 100 microliters of hydrochloric acid to each well. Measure the absorbance at 450 nanometers using a microplate spectrophotometer.
Run all samples in duplicate and include positive controls from recovered COVID-19 patients. The number of blood donors varied before, during, and after lockdown, and were lower than usual due to COVID-19 pandemic. Of the tested 3, 825 serum samples, 173 tested positive for anti-SARS-CoV-2 IgG antibodies while 3, 652 tested negative.
Overall, among the three study periods, the highest sero-positivity rate was observed after easing the lockdown, with 111 out of 848 samples testing positive. In contrast, the highest sero-negative rate was observed before the lockdown, with 1, 487 out of 1, 495 samples testing negative. The micro-neutralization assay confirmed sero positivity of 147 ELISA-positive cases for SARS-CoV-2 while 26 were sero-negative.
To our knowledge, this is the first study in the country addressing the COVID-19 seroprevalence and different Our in-house ELISA and micro-neutralization protocol enhance the accuracy, reducing the false detection of SARS-CoV-2 antibody. Our research raised the question about asymptomatic transmission dynamic and long immunity vector and how similar seroprevalence can guide the future epidemic and pandemic events.
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Overview
This study assessed COVID-19 seroprevalence in Jeddah, Saudi Arabia, among healthy blood donors across pre-lockdown, during-lockdown, and post-lockdown periods. Of 3,825 samples, 4.5% tested positive for IgG antibodies, with a significant increase in seroprevalence post-lockdown.
Key Study Components
Area of Science
- Immunology
- Public Health
- Epidemiology
Background
- COVID-19 has led to widespread health concerns globally.
- Understanding seroprevalence is crucial for assessing immunity in populations.
- Jeddah, Saudi Arabia, has experienced varying COVID-19 restrictions.
- This study focuses on healthy blood donors to gauge seroprevalence.
Purpose of Study
- To assess the seroprevalence of IgG antibodies against SARS-CoV-2.
- To analyze changes in seroprevalence across different lockdown phases.
- To highlight the role of asymptomatic transmission in the spread of COVID-19.
Methods Used
- Blood samples were collected from healthy donors.
- ELISA and PCR methods were employed for testing.
- Statistical modeling was used to analyze the data.
- Samples were stored at -20 degrees Celsius before testing.
Main Results
- 4.5% of the samples tested positive for IgG antibodies.
- There was a significant increase in seroprevalence post-lockdown.
- The findings underscore the effectiveness of initial restrictions.
- Asymptomatic transmission played a crucial role in the pandemic.
Conclusions
- The study provides insights into COVID-19 immunity in Jeddah.
- It emphasizes the importance of monitoring seroprevalence over time.
- Further research is needed to understand long-term immunity.
Frequently Asked Questions
Executive Industry Relevance
Quantitative seroprevalence testing for anti-SARS-CoV-2 IgG in healthy donors provides critical insight into population-level immunity dynamics across pandemic phases. This approach enables biopharma teams to assess the impact of public health interventions and identify asymptomatic transmission risks, informing predictive models and translational research. Reliable antibody detection and confirmation workflows support risk-adjusted decision-making for future epidemic preparedness and vaccine strategy refinement.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables robust interrogation of immune response dynamics to SARS-CoV-2 exposure in diverse populations.
- Supports biological de-risking by confirming antibody presence and specificity using ELISA and micro-neutralization assays.
- Provides quantitative data to inform predictive confidence in immune surveillance and epidemiological modeling.
Screening & Assay Development
- Establishes validated serological assay platforms for high-throughput antibody screening in large cohorts.
- Demonstrates reproducibility and standardization through duplicate testing and positive controls.
- Facilitates scalable workflows for ongoing seroprevalence monitoring and assay platform reuse.
Translational & Preclinical Research
- Aligns serological findings with real-world transmission dynamics to inform translational biomarker strategies.
- Enables continuity from population surveillance to preclinical vaccine and therapeutic evaluation.
- Supports risk-adjusted advancement of immunological targets based on population-level antibody data.
Pipeline & Workflow Integration
This seroprevalence testing workflow bridges early discovery, assay development, and translational research by providing validated, quantitative immune readouts across pandemic phases.
- Discovery Biology: Supports hypothesis testing on immunity duration and asymptomatic transmission using population-level antibody data.
- Screening: Delivers standardized, reproducible ELISA and micro-neutralization outputs for reliable serological assessment.
- Analytics: Provides quantitative absorbance and confirmation data to compare seroprevalence across demographic and temporal variables.
- Translational Research: Informs biomarker alignment and preclinical model selection based on real-world immune response patterns.
- Enterprise Reuse: Establishes a reusable serological testing platform adaptable to future emerging infectious diseases.
Operational & Enterprise Impact
- Scientific Value: Enhances predictive confidence in immune surveillance and target validation.
- Operational Value: Delivers standardized, scalable, and reproducible serological testing workflows.
- Strategic Value: Informs go/no-go decisions for vaccine and therapeutic development based on population immunity trends.
- Portfolio Impact: Supports risk-adjusted prioritization of immunological targets and public health interventions.
Implementation Considerations
- Requires expertise in serological assay development and statistical data analysis.
- Needs access to high-throughput ELISA platforms, micro-neutralization assays, and biosafety infrastructure.
- Demands rigorous cross-team standardization for sample handling and assay execution.
- Adaptable to different population cohorts and emerging infectious agents with validated reagents.
- Dependent on robust sample collection logistics and data management systems.
