Claims that CDC’S PCR test can’t tell covid from flu are wrong

Posts circulating on Facebook and Instagram claim the Centers for Disease Control and Prevention will stop using its covid-19 test because it cannot differentiate between the covid virus and flu viruses.

"CDC has just announced they will revoke the emergency use authorization of the RT-PCR tests first introduced in 2/20," reads a July 25 post, which goes on to quote from the agency's lab directive: "CDC encourages laboratories to consider adoption of a multiplexed method that can facilitate detection and differentiation of SARS CoV-2 and influenza viruses." It continues: "Translation: They’ve been adding flu cases to Covid cases when using that test."

Mike Huckabee, a former Fox News host who was also a Republican presidential candidate and governor of Arkansas, similarly claimed on Facebook that the CDC test cannot tell the difference between coronaviruses and flu viruses.

A July 24 Instagram post went further: “The FDA announced today that the CDC PCR test has failed its full review. Emergency Use Authorization has been REVOKED.”

The posts were flagged as part of Facebook's efforts to combat false news and misinformation on its news feed. (Read more about PolitiFact's partnership with Facebook.)

We wanted to know whether there was any truth to the idea that the CDC was removing its test because it is faulty and cannot tell one virus from another. So we consulted several laboratory testing experts.

The real reason for withdrawing the EUA request

The first Facebook post we referenced quoted from and linked to a July 21 CDC laboratory alert that informed labs that as of Dec. 31 the agency would withdraw its emergency use authorization request for the CDC 2019 Novel Coronavirus (2019-nCoV) Real-Time Reverse Transcriptase (RT)-PCR Diagnostic Panel or, for short, the CDC 2019-nCoV RT-PCR.

It is standard practice for the Food and Drug Administration to issue temporary emergency use authorizations for tests and other medical products that have not yet undergone the FDA's full approval process but need to be used in an emergency to diagnose, treat or prevent serious diseases.

The FDA issued the EUA for the CDC's 2019-nCoV RT-PCR in February 2020. At that time, no other tests were available in the U.S. to determine whether someone had covid.

But it's important to remember that what the CDC developed and submitted for its EUA request was not a tangible product but rather a protocol for how to test for covid, saidSusan Whittier, a professor of pathology and cell biology at Columbia University Irving Medical Center. That means the CDC wrote out directions specifying which reagents were needed to test the laboratory samples for the presence of the covid virus. The CDC does not distribute covid tests.

"It's not like they have a test that laboratories can purchase. We borrow their protocol and use the reagents that they say," said Whittier, who recently retired as director of the clinical microbiology lab at Columbia. So withdrawing the EUA request just "means that protocol will no longer be available."

In the lab alert, the CDC said it was withdrawing the EUA request because, rather than testing only for the covid virus, it wants labs to test people for multiple viruses simultaneously, using what is known as "a multiplexed method." The CDC's 2019-nCoV RT-PCR panel tests only for the covid virus.

"Such assays can facilitate continued testing for both influenza and SARS-CoV-2 and can save both time and resources as we head into influenza season," noted the alert regarding the multiplexed method.

Dr. Christopher Polage, an associate professor of pathology at Duke University, said his take on the CDC's message is that, because flu season is on the horizon, a patient might come in with respiratory symptoms that could be attributed to either covid or the flu. Laboratories need to start testing for both covid and various flu viruses.

But the lab alert does not mean the CDC's test cannot differentiate between covid and the flu.

In fact, the CDC's 2019-nCoV RT-PCR test was developed to look for the presence of a nucleic acid found only in the covid virus, said Kelly Wroblewski, director of infectious disease programs at the Association of Public Health Laboratories.

"It is not remotely accurate that the CDC test doesn't differentiate between flu and SARS-CoV-2. It doesn't detect influenza. It only detects SARS-CoV-2," said Wroblewski. "If flu and covid are both circulating, you would be able to detect only SARS-CoV-2 and not flu."

How the CDC's 2019-nCoV RT-PCR test (or any other PCR test) works, Wroblewski said, is that primers, which are little bits of a genetic material, are used to identify specific viruses. In this case, the primer is built to identify a nucleic acid found only in the covid virus.

If the covid virus is present in the sample, the primer will attach to the virus's nucleic acid and make many copies of it. A chemical in the test will then fluoresce, which the polymerase chain reaction, or PCR, machine will interpret as a positive result. If the covid virus is not present, the primer will have nothing to attach to.

When asked about the CDC withdrawing its EUA request, FDA spokesperson Jim McKinney told us PCR tests are considered the "gold standard" for covid diagnosis. He pointed us to data that illustrated the specificity and exclusivity of the CDC's test. That data shows test results came back negative for samples that contained similar viruses, including different types of flu and other coronaviruses.

All of this means the CDC's 2019-nCoV RT-PCR test would not erroneously detect flu viruses. Thus, the Facebook posts' assertions that the test cannot differentiate between covid and flu is demonstrably false.

Even though the CDC is withdrawing its EUA request for this specific test, Wroblewski pointed out, it still has an EUA for a second PCR test, a multiplex one that simultaneously tests for covid and influenza types A and B.

The FDA has issued EUAs to many laboratories and testing companies for hundreds of covid tests that use the same PCR technology the CDC uses — which experts said essentially made the CDC testing protocol moot, since similar tests will still be available.

So, while it is true the CDC is withdrawing its EUA request for its test that tests solely for covid, it is not for the reasons given by the Facebook posts. The assertion that covid case counts were inflated because the test was faulty and was counting flu cases as covid cases is false.

"They didn't withdraw the EUA because the test wasn't working," said Whittier. "They just wanted people to look for other viruses as well."

Polage agreed.

"The CDC is pulling their test 'off the market' as a gesture to encourage labs to use tests that include reagents (primers and probes) for both SARS-CoV-2 and Influenza so providers, labs, states, and CDC will have better data this fall and winter to estimate how much of clinical influenza-like illness is due to SARS-CoV-2 and how much is due to seasonal influenza," Polage said in an email.

Our ruling

Social media posts claimed the CDC was revoking its emergency use authorization request for its covid test because it couldn't differentiate between the covid virus and flu viruses. While the CDC is withdrawing its EUA request for the 2019-nCoV RT-PCR test, it is not because the test is faulty.

Rather, it's because the agency is concerned that, with flu season approaching, patients with respiratory illness symptoms should be screened for both the flu and covid. The patients shouldn't be tested for covid alone, because flu cases might be missed.

The statements made in these Facebook posts are not accurate. We rate this claim False.

This article was reprinted from khn.org with permission from the Henry J. Kaiser Family Foundation. Kaiser Health News, an editorially independent news service, is a program of the Kaiser Family Foundation, a nonpartisan health care policy research organization unaffiliated with Kaiser Permanente.