It is conducted by a nasal swab and immediately tested in the doctor’s office or other point-of-care location, producing diagnostic results within minutes by quickly detecting proteins found on or within the virus. In a statement announcing the emergency authorization of Quidel Corp.’s kit, the FDA said that antigen tests are cheaper to produce, simpler to conduct and easier to implement at scale than the current testing apparatus, which has relied on polymerase chain reaction (PCR) tests that detect genetic material from the virus.
Antigen tests are “important in the overall response against covid-19” and can “potentially scale to test millions of Americans per day” once other manufacturers enter the market, the FDA statement said. The FDA said it anticipates authorizing more antigen tests in the near future.
“It’s a really important tool,” said Amesh Adalja, an infectious disease physician and senior scholar at Johns Hopkins University Center for Health Security. “This is now the next step in simplifying testing.”
Quidel Corp. said that its test, called the Sofia 2 SARS Antigen FIA, can produce results within 15 minutes. The test cartridges can be placed in its Sofia 2 machine or manually developed on a countertop. Quidel is already shipping the test kits to customers, the company said in a statement.
Though rapid detection PCR tests have been used around the country, they are still more expensive and complex than the new test, experts say.
One major benefit of the antigen test is that it “allows us to arm our healthcare workers and first responders with a front line solution for covid-19 diagnosis,” Douglas Bryant, president and chief executive of Quidel Corp., said in a statement.
The FDA has authorized three different tests to help detect, diagnose and track the spread of the novel coronavirus: the antigen test, the PCR test and an antibody screening, which, unlike the first two tests, does not diagnose an active case of the virus but detects antibodies to it, which signal that the person was previously infected and has developed an immune response.
Put together, the three tests could offer a path forward for more widespread and thorough screening as Americans nationwide prepare to navigate safe returns to their jobs and the reopening of amenities that will place them in close contact with others.
Deborah Birx, the White House coronavirus response coordinator, has said in recent television appearances and news briefings that antigen testing was the kind of “huge technology breakthrough” the country needed to be able to “screen large numbers of individuals quickly.” She said that health-care officials and providers were simply unable to achieve that kind of scale with the PCR test.
A drawback of the antigen test, however, is that it is less reliable than the PCR test because it is not as sensitive, the FDA said. Positive results are “highly accurate,” but a negative result does not necessarily rule out the presence of the virus.
To backstop a potential false negative, the FDA said in the release that all negative antigen tests should be confirmed with a PCR test — a common protocol for antigen testing of other infections.
Former FDA commissioner Scott Gottlieb, who has been calling for a coronavirus antigen test since January, said that the new screening method should theoretically increase accessibility to testing for the average American because the machines used to process the kits are already sitting in doctor’s offices nationwide.
But, he added, that accessibility also hinges on an individual doctor’s willingness to open their office to potential viral exposure. Gottlieb warned that if the protocol following detection of a positive case is too onerous, providers might be reluctant to test and instead continue to refer patients to designated testing sites.
“What the CDC needs to do is come out with blanket guidelines that can apply to any doctor’s office,” Gottlieb said.
Last month, the World Health Organization issued a statement of “advice” for health-care providers and officials, saying they applauded the innovative efforts of test developers but that they did not recommend the use of antibody or antigen tests outside a research setting.
“Inadequate tests may miss patients with active infection or falsely categorize patients as having the disease when they do not, further hampering disease control efforts,” WHO officials said.
Gottlieb said antigen testing is “one piece of the puzzle."
“We need these kinds of tests,” he said. “This is a nice complement to the overall testing platform in this country.”