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Fact check: A cold, the flu or a flu shot won't cause positive tests for novel coronavirus

Camille Caldera, USA TODAY
·5 min read

The claim: The common cold, flu and flu vaccine will all result in positive COVID-19 tests

Before Thanksgiving, New York and Boston saw lines for COVID-19 tests that stretched for blocks and had hourslong waits.

But not everyone is clamoring for a test.

Numerous users on social media have claimed that coronavirus tests are inaccurate and ineffective and encouraged their followers not to take or trust them.

"A positive test for COVID-19 only means you have antibodies for the flu and/or the common cold," reads a post on Instagram. "DONT TAKE THE TEST!"

"Stop testing yourselves!!! If you've had a cold (coronavirus) you will test positive for COVID 19. If you've had the flu. You will test positive for COVID. If you've been vaccinated for influenza, you will test positive for COVID," reads a post on Facebook.

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The users behind the posts did not respond to requests from USA TODAY for comment.

Fact check: What's true and what's false about coronavirus?

The common cold and COVID-19 tests

This isn't the first time internet users have alleged a link between the common cold and positive COVID-19 tests. USA TODAY debunked a similar claim in July.

Fact check: Common cold does not produce positive coronavirus test

The claim that the common cold will produce a positive COVID-19 test relates to antibody tests.

Those check the blood for antibodies – disease-specific proteins produced by white blood cells to fight a virus – and reveal whether an individual had a past infection.

According to the Centers for Disease Control and Prevention, "a positive test result shows you may have antibodies from an infection with the virus that causes COVID-19. However, there is a chance that a positive result means you have antibodies from an infection with a different virus from the same family of viruses (called coronaviruses)."

It's true that the common cold is in the coronavirus family.

Dr. Lee Riley – head of the Division of Infectious Disease and Vaccinology at the University of California, Berkley – confirmed to USA TODAY that "about a third of the common cold is caused by coronavirus strains that are distinct from the COVID-19 coronavirus."

Still, he said, it's unlikely that having contracted the common cold would result in a positive test for COVID-19 antibodies.

"These common cold coronavirus strains would not induce an antibody response high enough to be mistaken for the antibody response against the COVID-19 virus," he wrote in an email. "If they did, almost everyone on the planet would be shown to have an antibody against COVID-19."

Antibody tests are not intended for diagnostic purposes. Diagnoses are based on viral tests.

According to the Food and Drug Administration, there are two kinds of viral tests for COVID-19 that can be used for diagnostic purposes: molecular tests and antigen tests.

Molecular tests detect the virus’s genetic material, and antigen tests detect specific proteins from the virus.

COVID-19 is a specific type of coronavirus with distinct genetic material and proteins.

That's why the CDC notes on its site that "other coronaviruses cannot produce a positive result on a viral test for SARS-CoV-2."

At-home testing could transform the fight against the novel coronavirus.
At-home testing could transform the fight against the novel coronavirus.

The flu, the flu shot and coronavirus tests

Though some symptoms of the flu and COVID-19 are similar, the viruses are distinct. The flu is caused by an influenza virus, not a coronavirus.

Riley told USA TODAY that claims about the flu and coronavirus tests are "nonsensical."

"The influenza virus is very different from the COVID-19 virus and would never induce an antibody response that would be mistaken for the COVID-19 virus antibody," he wrote.

Flu vaccines do not contain any types of coronaviruses, according to WUSA9.

Having contracted the flu or received a flu vaccine will not produce a positive result on a diagnostic test for the novel coronavirus.

A spokesperson for the FDA told FactCheck.org that all FDA-authorized tests for the coronavirus are specifically checked for cross-reactivity with influenza virus. They have not observed cross-reactivity with any of the tests.

Dr. Stephen Morse, a professor of epidemiology at Columbia University Medical Center, told USA TODAY that "no test for this virus can get approval if it gives false positives with other common respiratory viruses."

"Part of the original validation procedure for all the approved tests was to check a number of other respiratory viruses, like influenza and the common human coronaviruses, to make sure they didn’t give false positives," he said.

Morse emphasized that any positive test for the coronavirus should be taken seriously.

"Testing positive is convincing evidence that someone is infected and able to infect others," he wrote.

Our rating: False

Based on our research, the claim that the common cold, flu and flu vaccine will all result in positive tests for the novel coronavirus is FALSE. None will produce a positive result. Viral tests for the coronavirus detect its distinct genetic material or proteins – so other viruses won't cause false positives. It's possible that the common cold will produce a positive result in an antibody test, but those aren't used to diagnose COVID-19.

Our fact check sources:

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Our fact check work is supported in part by a grant from Facebook.

This article originally appeared on USA TODAY: Fact check: Cold, flu, flu shot will not cause positive COVID-19 tests