COVID-19 antibodies could remain stable in an infected person's blood for two months after diagnosis, according to a newly published study.

The researchers from St. George’s University of London also said antibodies were not detected in all of the infected participants, however, which could contribute to discussions on best practices for interpreting results from antibody tests. Serological testing and the ability to detect viral antigens may increase diagnostic accuracy for COVID-19, study authors wrote, especially when antibody tests are negative but symptoms resemble those of COVID-19.

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The analysis found that 2 percent to 8.5 percent of infected individuals do not develop detectable antibody responses even weeks after infection. Also, seroconverters -- someone who has detectable antibodies -- were older than non-seroconverters, with a median age of 65.5 compared to 41 years.

The study was published in the preprint server medRxiv, meaning the preliminary report has not been certified by peer review.

Sanjeev Krishna, professor of molecular parasitology and medicine at St George’s, University of London, studies an assay. (Photo courtesy of St George’s, University of London)

"Our results provide an improved understanding of how best to use viral and antibody tests for coronavirus, especially when not every person exposed to the virus will have a positive response,” said Sanjeev Krishna, professor of molecular parasitology and medicine at St. George’s University of London, according to a university press release.

“We need to understand how best to interpret the results from these tests to control the spread of the virus, as well as identifying those who may be immune to the disease," he said.

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Researchers and clinicians analyzed antibody test results from 177 infected people. The study also found that patients with the most severe infections and the largest inflammatory responses were more likely to develop antibodies.

“The researchers suggest that this may be due to antibody responses working in parallel with an inflammatory response to severe disease, or that a higher viral load could lead to greater stimulation of the inflammatory and antibody development pathways,” according to the release.

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For those with negative antibody test responses, the researchers suggest other immune response mechanisms are at play, like different antigens or T-cells. Or perhaps relatively mild infections are restricted to certain areas of the body, they said, such as within mucosal cells of the respiratory tract.

Researchers also noted that “higher antibody responses (were) associated with non-white ethnicity,” building on knowledge that ethnic minority groups have a higher chance of developing severe disease.

Krishna hopes that sharing the data at an early stage will accelerate progress toward effective use of test results around the world.