The Use of Antibodies in COVID-19 Diagnostics, Treatment, and Post-Infection Serosurveillance

The COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, prompted an unprecedented global response in healthcare, science, and technology. Among the tools used to fight the disease, antibodies have played a vital role in diagnostics, treatment, and post-infection serosurveillance. These proteins, produced by the immune system, recognize and bind to specific viral components, providing a powerful mechanism for both detecting the virus and combating its effects.

This article explores the diverse applications of antibodies in the COVID-19 pandemic through five key areas: diagnostics, monoclonal antibody therapy, convalescent plasma treatment, vaccine development and evaluation, and serological surveillance.

Diagnostic Applications of Antibodies

Antibodies have been instrumental in the development of COVID-19 diagnostics, especially serological tests designed to detect past infections. While PCR tests detect viral RNA and are best for identifying active infections, antibody-based tests are useful for determining whether someone has previously been exposed to the virus.

Two main types of serological tests use antibodies:

  • Lateral flow assays (LFAs): These are rapid, point-of-care tests similar to pregnancy tests. They detect IgM and IgG antibodies in blood or serum, typically becoming positive within 1–3 weeks after infection.
  • Enzyme-linked immunosorbent assays (ELISAs): These are more sensitive laboratory-based tests that can quantify antibody levels, providing insights into the strength and duration of the immune response.

These tests were crucial in the early pandemic phase for understanding the spread of SARS-CoV-2 and helped identify asymptomatic or mildly symptomatic individuals who had recovered unnoticed.

Monoclonal Antibody Therapies

Monoclonal antibodies (mAbs) have emerged as a targeted therapeutic strategy for treating COVID-19, especially in high-risk patients with early-stage disease. These lab-engineered antibodies are designed to specifically bind to the spike protein of SARS-CoV-2, neutralizing the virus and preventing it from entering host cells.

Key monoclonal antibody therapies developed for COVID-19 include:

  • Regeneron’s REGN-COV2 (casirivimab and imdevimab)
  • Eli Lilly’s bamlanivimab and etesevimab
  • AstraZeneca’s Evusheld (tixagevimab and cilgavimab)

These therapies were shown to reduce hospitalization and death in high-risk populations when administered early. However, their effectiveness has waned with the emergence of new SARS-CoV-2 variants, some of which carry mutations that reduce antibody binding affinity. This has led to the need for continuous development and adaptation of monoclonal antibody treatments.

Convalescent Plasma Therapy

Before specific monoclonal antibodies were available, convalescent plasma therapy was used as a passive immunization method. It involves transfusing plasma from recovered COVID-19 patients into those currently battling the infection. This plasma contains a diverse mixture of antibodies, including those capable of neutralizing SARS-CoV-2.

Initial results from observational studies suggested some benefit, particularly when plasma was administered early in the disease course and had high antibody titers. However, randomized clinical trials yielded mixed results. The U.S. FDA granted Emergency Use Authorization (EUA) for convalescent plasma, but its use has since declined as more effective treatments, such as antivirals and monoclonal antibodies, became available.

Despite the variability in outcomes, convalescent plasma therapy contributed valuable knowledge to the understanding of antibody-mediated immunity against COVID-19.

Antibodies in Vaccine Development and Evaluation

The development of effective COVID-19 vaccines relied heavily on understanding how antibodies neutralize SARS-CoV-2. The spike protein, particularly the receptor-binding domain (RBD), was identified as the main target of neutralizing antibodies. Most vaccines—such as the mRNA-based Pfizer-BioNTech and Moderna, and adenoviral vector-based Oxford-AstraZeneca—use this protein to elicit an immune response.

Antibody testing also played a critical role in:

  • Measuring vaccine efficacy: Levels of neutralizing antibodies in vaccine recipients serve as a correlate of protection.
  • Assessing booster needs: Waning antibody levels over time have informed public health decisions regarding the timing of booster shots.
  • Tracking immune escape: The appearance of variants with mutations in the spike protein has prompted studies on antibody neutralization capacity post-vaccination.

These evaluations not only guided vaccine deployment but also shaped strategies to combat emerging variants like Delta and Omicron.

Post-Infection Serosurveillance and Population Immunity

Beyond individual diagnosis and treatment, antibodies have served a crucial role in population-level studies through serosurveillance. Seroprevalences surveys estimate the percentage of people in a population who have antibodies to SARS-CoV-2, providing insight into how widespread the virus has been and how much immunity might exist within a community.

Serosurveillance data have been essential for:

  • Estimating infection rates, including asymptomatic cases
  • Monitoring the progression of the pandemic in different regions
  • Evaluating the impact of public health interventions
  • Predicting the likelihood of future outbreaks

For example, large-scale studies conducted by the CDC and other international health bodies tracked antibody prevalence across various demographics and geographies. These findings helped refine models of transmission dynamics and informed vaccine allocation strategies.

Furthermore, combining antibody data with vaccination records has allowed researchers to distinguish between natural infection and vaccine-induced immunity, enhancing our understanding of long-term protection.

Conclusion

The use of antibodies in the fight against COVID-19 has been multifaceted, encompassing diagnostics, treatment, vaccine development, and public health surveillance. Each application has contributed to mitigating the impact of the pandemic and expanding our understanding of immunological responses to SARS-CoV-2.

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