BD’s launch will be a test for the utility of COVID-19 antigen testing
The launch and scale-up of BD’s SARS-CoV-2 rapid antigen test will help reveal whether the modality strikes the right balance of speed, accessibility and reliability needed to fill critical holes in COVID-19 testing infrastructure.
Becton Dickinson and Co. (NYSE:BDX) announced Monday it received FDA Emergency Use Authorization (EUA) for its test to detect SARS-CoV-2 nucleocapsid protein antigens on a portable instrument that gives results in 15 minutes.
Its performance metrics and scale-up capacity are similar to that of the only other FDA-authorized COVID-19 antigen test, launched by Quidel Corp. (NASDAQ:QDEL) on May 8. Together, the companies’ outputs could provide the critical mass needed to gauge antigen tests’ place in the COVID-19 diagnostic armamentarium.
Unlike more commonly used COVID-19 molecular diagnostics that measure viral genomic material using nucleic acid primers or probes, viral antigen tests are immunoassays that detect SARS-CoV-2 proteins using tool antibodies (see “COVID-19 Diagnostic Tech Tableau”).
The advantage of these tests is that they can be more easily and cheaply geared to deliver rapid readouts at the point of care than nucleic acid-based diagnostics (see “Viral Antigen Tests on Deck”).
The modality’s speed and accessibility has made it a strategic priority for the U.S. government. But data from BD and Quidel suggests these tests are less sensitive than molecular diagnostics, and will require follow-up analyses to confirm negative results (see “White House Highlights COVID-19 Antigen Test”).
The balance between speed and sensitivity has already surfaced as an issue post-launch for at least two high-profile rapid tests: the ID NOW rapid molecular diagnostic from Abbott Laboratories (NYSE:ABT) and BD’s rapid test for patient antibodies against SARS-CoV-2, which was co-developed with BioMedomics Inc. BD and BioMedomics opted to withdraw their serological test and develop a version that meets standards FDA introduced after the test came on the market (see “Withdrawal, Reevaluation of Rapid COVID-19 Tests”).
Crunching the numbers
The analytical sensitivity of BD and Quidel’s antigen tests are reflected in their limits of detection (LoDs), defined as the lowest amount of the target that the test can detect at least 95% of the time. A lower LoD indicates a more sensitive test.
According to BD’s information for use (IFU) document, its SARS-CoV-2 antigen test has an LoD of 140 TCID50/mL, similar to the LoD of 113 TCID50/mL reported by Quidel.
These values are about 1,000 times higher than those of nucleic acid tests previously authorized by FDA that reported LoDs in terms of TCID50. TCID50 represents the viral load at which 50% of cells are infected when a solution containing the virus is added to cell culture (see “Limits of Detection for New Coronavirus”).
When evaluated for clinical sensitivity and specificity by comparison to an FDA-authorized molecular diagnostic, BD’s test had a positive percent agreement (PPA)/sensitivity of 84%, and a negative percent agreement (NPA)/specificity of 100% across samples from 226 prospectively enrolled symptomatic patients. Quidel similarly reported PPA/sensitivity and NPA/specificity values of 80% and 100%, respectively.
BD has an installed base of 25,000 instruments across the U.S. and plans to produce 2 million tests per week by the end of September, with a total of 10 million tests between July and September. FDA has deemed its test CLIA waived, which means it can be performed in a wide range of settings including retail pharmacies.
According to a May 26 Quidel investor presentation, the company is ramping up to produce 1.5-1.8 million COVID-19 antigen tests per week. The company has an installed base of about 43,000 instruments worldwide.
SARS-CoV-2 N - SARS-CoV-2 nucleocapsid protein