Scientists develop safe, rapid Covid-19 antibody test

Scientists have developed a rapid test to detect antibodies in Covid-19 patients that specifically block the novel coronavirus, an advance that may lead to faster methods for estimating the population level infection rate of the disease.

According to the study, published in the journal Nature Biotechnology, a rapid test to detect neutralising antibodies -- capable of blocking the novel coronavirus SARS-CoV-2 -- is urgently needed to facilitate monitoring of infection rates, as well as to determine vaccine efficacy during clinical trials.

In order to facilitate this, the researchers, including those from the Duke-NUS Medical School in Singapore, developed a new assay which is much faster than conventional tests for neutralising antibodies, taking only one or two hours to complete.

They said the new method, validated in two groups of patients who had Covid-19 from Singapore and Nanjing, China, does not require the use of the live virus.

According to the scientists, the current gold standard assay for detecting neutralising antibodies requires the handling of live SARS-CoV-2 in a biosafety level three laboratory containment facility, and is time-consuming, taking two-four days to complete.

Another method involving a pseudovirus-based neutralisation test to detect such antibodies can be done in a biosafety level two laboratory, they said, but added that this too requires the use of live viruses and cells.

In the current research, the scientists Lin-Fa Wang, Danielle Anderson, and their colleagues designed a surrogate virus neutralisation test that does not require the use of any live virus or cells.

"The surrogate virus neutralisation test does not require biosafety level three containment, making it broadly accessible to the wider community for both research and clinical applications," the researchers wrote in the study.

They said the new test takes only one to two hours to complete, and can be conducted in a biosafety level two laboratory.

The researchers used the purified part of the viral spike protein which binds to the host cell's surface receptor ACE2 to mimic the virus-host interaction.

According to the scientists, this interaction can be blocked by specific neutralising antibodies in patient or animal sera in a similar manner to the conventional virus neutralisation and pseudovirus-based tests.

The study noted that this assay can also differentiate neutralising antibodies from those which bind to the spike protein, but do not block the virus.

Following the lab findings, the scientists validated the new assay with two separate groups of patients recovering from Covid-19: 175 patients who had Covid-19 and 200 healthy controls in Singapore, and 50 patients who had Covid-19, and 200 healthy controls in Nanjing.

They said the test can distinguish between antibody responses to Covid-19, and to other human coronavirus infections such as the one causing common cold.

According to the study, the assay achieves 99.93 percent specificity and 95–100 percent sensitivity.

When the researchers studied the specificity of their test for SARS-CoV-2, versus the 2002-03 SARS pandemic virus using serum collected from patients who had recovered from the earlier coronavirus outbreak, they noted that SARS-neutralising antibodies were still detectible 17 years later.

Although the surrogate virus neutralisation assay may never be able to completely replace the conventional virus assay, they said it performs well, and in some cases may be easier to use for many aspects of Covid-19 research.