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Quidel’s antigen test OK’ed with promise of fast COVID checks

Jennifer A. Dlouhy and Katerina Petroff

The U.S. Food and Drug Administration has approved a new antigen test that could help rapidly screen people infected with COVID-19.

The emergency use authorization — the first ever for a COVID-19 antigen test — was granted late Friday to San Diego-based Quidel Corp., the company and the agency said.

The move could be a breakthrough in screening for the novel coronavirus, coming as state and local governments ease lockdown orders and businesses begin reopening across the nation — and health professionals argue that swift screening is essential to temper new outbreaks.

Dr. Deborah Birx, a member of the White House coronavirus task force, said in April that a “breakthrough innovation” in antigen testing was needed to speed reopening of the U.S. economy.

“We have to be able to detect antigen, rather than constantly trying to detect the actual live virus, or the viral particles itself, and to really move into antigen testing,” Birx said April 26 on NBC’s “Meet the Press.”

Existing diagnostic screening for active infections relies on polymerase chain reaction tests designed to detect genetic material from COVID-19. While accurate, those tests take time to run and analyze.

By contrast, tests like the just-approved Quidel one are meant to rapidly deliver results by detecting antigens — the proteins located on the outer surface of the coronavirus that trigger an immune response in the body.

Antigen tests can generally be produced at a lower cost than their slower-to-analyze PCR competitors, and their simpler design could allow manufacturers to produce enough to test millions of Americans per day, the FDA said in a news release.

While test results can come within minutes, the FDA warned that they are far from foolproof, with a higher chance of false negatives. The World Health Organization has made similar observations.

“Antigen tests are very specific for the virus, but are not as sensitive as molecular PCR tests,” the FDA said. “This means that positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection.”

While the antigen tests have lower sensitivity then certain other devices, they’re inexpensive and easy to use, Dr. Scott Gottlieb, the former FDA commissioner, said on Twitter.

The FDA said it expects more antigen tests to be authorized for COVID-19, and the agency said it would provide a template to guide future approvals.

A third type of tests — antibody tests — use blood to look for proteins that are markers of a previous coronavirus infection. They work by identifying antibodies that were produced by the body’s immune system in response to an earlier infection. Although they can detect an active infection, the FDA says these serological, or antibody, tests should not be used that way.

Shares in Quidel have more than doubled in 2020 so far, closing Friday at $158.60, driven by optimism about the diagnostic health care company’s role in COVID-19 testing.

The new approval is specifically for Quidel’s Sofia 2 SARS Antigen FIA.