Researchers at the National Institute of Standards and Technology (NIST) have produced synthetic gene fragments from SARS-CoV-2, the virus that causes Covid-19. This material, which is noninfectious and safe to handle, can help manufacturers produce more accurate and reliable diagnostic tests for the disease.

Tests for an active infection—as opposed to antibody tests that indicate a past infection—work by detecting the virus’s genes on a nasal swab. But a negative result does not necessarily mean that a person is disease-free. It could be that the amount of virus is too low for the test to detect, which is especially possible during the first days after catching the virus.

“Having better data on test sensitivity will help us understand how often tests for Covid-19 produce a negative result for people who are actually infected,” says NIST research scientist Megan Cleveland.

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