French Variant of COVID-19 Undetectable in PCR Test

It was only diagnosed after a biopsy.

As if the world needed another bit of COVID-related bad news, another difficult strain of COVID-19 turned up in France that has the special ability to fool the gold-standard polymerase chain reaction (PCR) tests. 

The new strain was nicknamed “le variant breton” after Brittany, the region in France where it was first discovered. On March 17, the Ministry of Health revealed there were eight of 79 COVID-19 patients who were infected with the new strain but weren’t initially tagged as positive. All eight patients have since died.


Patients Tested Negative Despite Having Symptoms

According to a report by Forbes, the eight patients who were infected with the French variant of COVID-19 all tested negative in the gold-standard PCR tests despite exhibiting symptoms. 

A PCR or polymerase chain reaction test is a very sensitive test that is considered the global gold-standard in detecting active cases of COVID-19. It uses a chemical reaction to create millions of copies of a virus’s genetic material, enough to trigger another chemical reaction that produces a fluorescent light. This light is the signal that indicates you have an active infection. 

In some cases, the PCR test is too effective, it is able to pick up dead COVID-19 viruses being shed by a patient’s body, and interprets this as an active infection, resulting in a false-positive test result. 

In the case of the French variant of COVID-19, the virus somehow evades detection through PCR tests. The eight patients were only diagnosed with COVID-19 after tissue samples from their respiratory system and blood samples were collected and analyzed. 


According to Joshua Cohen, an independent healthcare analyst, the French variant may have evolved specifically to bypass detection through PCR tests. But there’s a silver lining: it could be less transmissible. 

“Preliminary research results do not indicate the new mutation causes more severe disease or is more contagious than other known variants,” wrote Cohen. But he also says more research is needed to establish this.

As of this writing, it is unknown whether the French variant of COVID-19 affects the efficacy of vaccines. 

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Mario Alvaro Limos
Features Editor-at-Large
Mario Alvaro Limos is features editor-at-large at Esquire Philippines, and heads the Lifestyle and Esports content of as its section editor. Email him at [email protected] and [email protected]
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