The FDA added two new types of tests to help diagnose SARS-CoV-2 infection, adding to its pile of diagnostic Emergency Use Authorizations (EUAs), which could help states shore up their testing capacity amid reopening and help employers and providers as workers and patients return.
On May 8, the FDA granted an EUA to the first antigen test to diagnose infections of SARS-CoV-2, which causes COVID-19. Like other diagnostic tests granted EUAs thus far, the test relies on nasal and/or nasopharyngeal samples. However, the test detects the presence of the nucleocapsid viral antigen and can deliver a result within 15 minutes.
Previous in vitro diagnostics that were granted an EUA have relied on rtPCR, which requires more time to extract the RNA and conduct the test. The antigen test can be performed at the point of care in a CLIA-certified facility or lab.
However, according to the documentation for the test, negative results should be treated as presumptive and confirmed with a molecular assay.
“Antigen tests are very specific for the virus, but are not as sensitive as molecular PCR tests. 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,” Drs. Stephen Hahn and Jeffrey Shuren wrote in a memo announcing the EUA. Hahn is the FDA commissioner; Shuren is the director of the agency’s Center for Devices and Radiological Health (CDRH).
On Monday, the FDA released an EUA template for antigen tests to streamline the development of similar tests. The agency had already issued templates for in vitro diagnostics as well as serology tests.
The May 7 authorization of the first saliva-based test could help accelerate sample collection. In April, the FDA granted an EUA to a home-based test that relies on self-collected nasal samples.
The saliva-based test “provides an additional option for the easy, safe and convenient collection of samples required for testing without traveling to a doctor’s office, hospital or testing site,” Hahn said in the memo announcing the EUA.
The molecular test allows the patient to collect the sample with a kit that can be returned to the laboratory, which is the only site approved to carry out the test and analyses.
The use of a saliva-based test could also address another sample collection challenge that hospitals and healthcare workers have faced: a shortage of swabs, which has reportedly held up testing in some states such as California.
As of Tuesday, the FDA has authorized over 65 in vitro diagnostics for SARS-CoV-2 since the public health emergency was declared in February, with two-thirds of those coming in the past six weeks. These tests are different from the serology tests, which can determine whether an individual has been exposed to the virus and developed antibodies against it.
The agency has issued just 12 EUAs for serology tests and recently had to clarify its policy after numerous unauthorized tests flooded the market.
While the FDA has been quick to authorize new diagnostic tests for COVID-19, states have faced challenges in ramping up their testing capacity as many start to reopen.
According to the CovidTracking.com project, 9.4 million tests have been reported in the US as of Tuesday. The number of daily tests has been steadily increasing, with a seven-day rolling average of nearly 300,000 tests conducted daily, according to the Johns Hopkins Coronavirus Resource Center.
A previous analysis by HRI found that testing per capita varied among some of the most populous and rural states, with the hardest-hit areas having more capacity.
While New York continues to have some of the highest per-day testing rates, with a May 10 seven-day average of 21,600, according to the Johns Hopkins resource center, other states such as Illinois have increased the number of tests conducted to 12,441 on May 10 compared to about 7,000 in mid-April. California has also nearly doubled its testing capacity, with a seven-day average of 36,233 on May 10 compared with 21,234 in mid-April.
Another factor in whether the states have enough testing is the positivity rate. According to the WHO, countries where the number of positive tests has been between 3% and 12% have conducted extensive testing. According to Johns Hopkins, the US positivity rate is around 7% but it varies widely by state. For New York, the rate was 8% on May 10; for New Jersey, it was 16%.
The CovidExitStrategy.org website tracks individual states based on the gating criteria outlined by the White House, which recommends a capacity of 500,000 tests per day. The site calculates the state’s per capita testing benchmark to meet the goal along with several factors. As of May 14, North Dakota and Nebraska had met all the criteria.