FDA has greenlighted Quidel’s antigen test for detecting infection with the novel coronavirus, adding another option for the diagnostic response to the outbreak.
The emergency use authorization, which FDA disclosed Saturday, marks the first time the agency has given the nod to a SARS-CoV-2 antigen test for use in the U.S., potentially addressing the limitations of other COVID-19 testing.
Antigen-based diagnostics are cheaper to make than PCR tests and deliver results far faster, meaning their widespread availability could enable the U.S. to test millions of people a day and detect infections sooner.
The diagnostic response to the coronavirus pandemic has so far focused on two types of tests. Laboratories have run PCR assessments of samples taken by swabs to show if a person is infected by the coronavirus. The second type of diagnostic, known as serology tests, look for antibodies against the virus to show if a person has previously been infected and therefore may have some degree of immunity.
While the existing tests can detect active and prior infections, the shortcomings of PCR tests mean there is scope to further improve the diagnostic arsenal. PCR tests are very accurate but they are neither cheap nor fast, making them ill-suited for the task of quickly determining the infection status of millions of Americans per day. That task could be an important contributor to safely open up the U.S. economy in the absence of a vaccine.
On paper, antigen tests are better suited to the task. Unlike PCR tests, which detect viral genetic material, antigen-based diagnostics are designed to determine if a sample contains proteins found on the surface of the coronavirus, enabling them to deliver results in minutes rather than days.
The FDA emergency use authorization covers Quidel’s SARS Antigen FIA. The test runs on Sofia 2, an instrument that uses fluorescent chemistry to deliver a result in 15 minutes.
Quidel is yet to discuss the pricing of its product but FDA expects antigen-based diagnostics to be cheaper to make than PCR tests, resulting in a combination of speed and price that could support population-scale testing. FDA will need to authorize other tests, such as those in development at E25Bio and OraSure Technologies, before enough antigen-based diagnostics are available for mass testing. The agency is working on an EUA template to help other antigen tests come to market.
FDA said the speed and cost of antigen tests could make them vital in the response to COVID-19 but it acknowledges the approach has weaknesses. Antigen tests are more likely to deliver false negatives than PCR diagnostics, meaning it will be impossible to have full confidence in a negative result until it is confirmed by the slower, more expensive approach.
Analysts from Craig-Hallum in a note Monday reiterated their buy rating on Quidel arguing that "COVID could be at least a 3-year benefit" to the company with the potential to generate $1 billion in cash during this timeframe.
William Blair analysts called the EUA granted to Quidel the "most impactful and game-changing news in COVID-19 testing to date" which they contend could add more than 1 million tests per week on a U.S. installed base of 36,000 instruments, two-thirds of which are Sofia 2 instruments.
At the same time, Craig-Hallum analysts acknowledged that the Quidel test only has 80% sensitivity compared to more than 90% sensitivity from molecular diagnostics. "However, a public health crisis demands speed, and is partly the reason why antigen is the standard of care for flu every year."