Question

Which of the following is an established use of accurate antibody tests for SARS-CoV-2?

1. Diagnosis
2. Establishing the proportion of a population who have been infected with SARS-CoV-2
3. Establishing immunity to reinfection
4. None of these are accurate statements.

Answer 1

B)Establishing the proportion of a population who have been infected with SARS-CoV-2

SARS-CoV-2, which causes the COVID-19 disease, is a novel coronavirus which results in an acute respiratory syndrome. Studies have shown that SARS-CoV-2 virus enters the host cells via its spike (S) protein, which has a distinct furin cleavage site, by binding to the human cell surface ACE2 protein (1,2). The binding triggers receptor-induced conformational changes to expose the protease cleavage site in the spike protein to serine protease TMPRSS2. TMPRSS2 then cleaves and activates the spike protein, causing a viral infection.

Several groups are now independently evaluating antibody tests for these measures. One study, dubbed the COVID-19 Testing Project and run by physicians and researchers at institutions including the University of California, San Francisco (UCSF), the University of California, Berkeley (UCB), Massachusetts General Hospital (MGH), and the Chan Zuckerberg Biohub, evaluated 10 LFAs and two ELISAs. To assess their ability to identify antibodies against SARS-CoV-2, the team used plasma or serum samples from three groups: 80 people who had shown symptoms of COVID-19 and had tested positive using a PCR-based screen, 52 who had a respiratory infection but were found to be infected with another virus or had tested negative on a PCR test for SARS-CoV-2, and 108 blood donors whose samples were drawn in 2018 or earlier, before the pandemic began.

Their assessment found that the ability to detect antibodies in people who had tested positive for the virus increased over time, rising to 81–100 percent when more than 20 days had elapsed since symptoms began, depending on the product. One of the members of the team, Patrick Hsu, a bioengineer at UCB, notes that this finding highlights why longitudinal antibody testing is important, given that a negative result may mean a person had been exposed to the virus but hadn’t yet developed a detectable level of antibodies. On the specificity side, the proportion of false positives found in the pre–COVID-19 samples ranged from 0–16 percent. The agreement between the findings of LFAs and ELISAs ranged from 75–94 percent. The team posted its results as a preprint on the project website on April 24. Alex Marson, an immunologist at UCSF and a coauthor of the report, cautions that some numbers, especially for tests’ ability to detect antibodies in positive cases, may be revised as his team continues to analyze the data.
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