Over-the-counter Covid tests can quickly show whether a person is infected with SARS-CoV-2. But if you have a positive result, there’s no equivalent at-home test to assess how long you’re protected against reinfection, said researchers from Johns Hopkins University, MIT and Harvard University.
It is because vaccines against Covid infection can guard against future infections for a while, but it’s unclear exactly how long that protection lasts.
A good indication of immune protection is a person’s level of antibodies, but the gold standard measurement — the enzyme-linked immunosorbent assay (ELISA) — requires expensive equipment and specialised technicians.
The new readily available glucose meter, described in the Journal of the American Chemical Society, are easy to use and can be integrated with remote clinical services.
In the study the team wanted to see whether producing a fusion protein consisting of both invertase and a detection antibody would work in an assay that would allow SARS-CoV-2 antibody levels to be read with a glucose meter.
The researchers designed and produced a novel fusion protein containing both invertase and a mouse antibody that binds to human immunoglobulin (IgG) antibodies. They showed that the fusion protein bound to human IgGs and successfully produced glucose from sucrose.
Next, the team made test strips with the SARS-CoV-2 spike protein on them. When dipped in Covid-19 patient samples, the patients’ SARS-CoV-2 antibodies bound to the spike protein.
Adding the invertase/IgG fusion protein, then sucrose, led to the production of glucose, which could be detected by a glucose meter. They validated the test by performing the analysis with glucose meters on a variety of patient samples, and found that the new assay worked as well as four different ELISAs.
The researchers said that the method can also be adapted to test for SARS-CoV-2 variants and other infectious diseases.