U.S. approval of a new antigen test to rapidly screen people for the coronavirus “is a real game-changer,” said the former head of the U.S. Food and Drug Administration.

The emergency use authorization — the first ever by the FDA for a COVID-19 antigen test — was granted to San Diego-based Quidel Corp. late Friday, according to a notice from the agency.

The move could mark a breakthrough in screening for the virus and comes as state and local governments ease lockdown orders and businesses begin reopening across the nation -- and as health professionals argue that swift screening is essential to temper new outbreaks.

“It’s a very rapid test that could be used in a doctor’s office,” former FDA Commissioner Scott Gottlieb said Sunday on CBS’s “Face the Nation.” “Doctors now have about 40,000 of these Sophia machines already installed in their offices” where they are used to test for strep throat and flu, he said.

Each test will probably cost about US$5, with results available within minutes, said Gottlieb, now a special partner at New Enterprise Associates, a venture capital firm that invests in the health-care and biotech sectors.

A big challenge will be what guidance is made by U.S. authorities about how doctors test in their offices, he said: “If turning over a positive case in your medical office means that you have to do a deep cleaning and quarantine your nursing staff and close your office, doctors aren’t going to be testing.”

Wanted: Innovation

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.

False Negatives

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’re far from foolproof, with a higher chance of false negatives. The World Health Organization has made similar observations.

The newly-approved test is about 85 per cent sensitive, said Gottlieb. In other cases, doctors who suspect a patient may have Covid-19 would order one of the PCR-based tests, which take about 24 hours to deliver results, he said.

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 US$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.

--With assistance from Katerina Petroff.