Researchers test commercial assays to detect SARS-CoV-2 antibodies six months after infection

The coronavirus disease 2019 (COVID-19) pandemic continues as many parts of the world grapple with skyrocketing cases. The global toll has reached 72.4 million cases, and 1.61 million have lost their lives. Caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), COVID-19 can cause a wide array of symptoms, including a persistent dry cough, fever, loss of smell or taste, and breathing difficulty.

Like other pathogens, being infected with SARS-CoV-2 induces host immune responses that work to clear the virus and prevent reinfection. This means that, in theory, if a recovered patient produces robust neutralizing antibodies and is re-exposed to the virus, they have a good chance of fending off reinfection. But as these neutralizing antibodies can wane over time, a big question scientists are currently grappling with is the length of time those recovered can retain a strong presence of neutralizing antibodies that help immunize them against SARS-CoV-2

Researchers at the Hospices Civils de Lyon (HCL) in France found that people infected with SARS-CoV-2 can develop antibodies that persist for up to six months. After testing commercial assays to detect antibodies, the Wantai antibody assay has a positivity rate of 100%.

These findings can help public health authorities navigate risks associated with re-exposure and reinfection as well as aid scientists in utilizing the best possible tools for determining the extent of the pandemic at the population level and the duration of robust antibody presence in recovered individuals.

The study

The study, published on the pre-print medRxiv* server, shows the level of antibodies present in healthcare workers at the University Hospital of Lyon in France. In doing so they sought to determine how long the protective effect of antibodies against SARS-CoV-2 lasts.

To arrive at the study’s findings, the researchers recruited 296 healthcare workers. They collected blood samples six months after the disease onset. Three commercial assays were used to test the samples:

  • The Wantai Ab assay detects total antibodies against the receptor-binding domain (RBD) of the spike protein
  • The bioMerieux Vidas assay detects immunoglobulin G (IgG) to the RBD
  • The Abbott Architect assay detects all samples with a virus neutralization assay (VNA) using the live virus

The team has found that the Wantai ab assay has the highest positivity rate of 100%, followed by the bioMerieux assay with a positivity rate of 84.8%, and the Abbott assay with a 55.4% positivity rate.

The researchers also found that only 51% of the healthcare workers were positive for neutralizing antibodies at six months. Less than 10% of the healthcare workers had a neutralizing antibody titer more significant than 80.

The study findings highlight the importance of commercial assays to detect antibodies against SARS-CoV-2. However, only the Wantai assay could be useful in detecting antibodies in the long term. VNA should remain the gold standard to evaluate the protective antibody response. For other commercial assays, they could be used as a first-line screening of neutralizing antibodies.

“Despite these observations on the decrease of neutralizing antibodies in patients with mild COVID-19, it is important to note that they do not preclude the protective role of an anamnestic antibody response in previously exposed subjects, nor that of the long-term cellular immunity,” the researchers explained.

Global situation

With the surging COVID-19 cases, it is crucial to determine how long antibodies against SARS-CoV-2 will last. This way, scientists can develop effective vaccines in the hopes of achieving herd immunity.

In the United Kingdom, the government has started vaccination with Pfizer’s COVID-19 vaccine. They prioritized the elderly, health care workers, and those at a higher risk of developing severe COVID-19.

As vaccination efforts have started in some countries, the number of cases continues to increase.

The United States remains the country with the highest number of cases, topping 16.24 million cases and more than 299,000 deaths.

India and Brazil follow with a staggering 9.85 million and 6.90 million cases, respectively. Other countries with high case tolls include Russia, France, and the United Kingdom, with over 2.62 million, 2.43 million, and 1.85 million cases, respectively.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Angela Betsaida B. Laguipo

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.


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