A new coronavirus variant found in France can hide from COVID-19 nasal-swab tests

• France's health ministry has identified a new coronavirus variant that can evade some tests.
• So far, that variant doesn't seem to be deadlier or more infectious than other strains.
• The variant shares some mutations with another variant first found in California.

A region of France has been beset by a version of the coronavirus that can hide from standard tests.

The French ministry of health and social affairs announced Monday that among a cluster of 79 COVID-19 cases in Brittany, eight patients were infected with the new variant, but several of them tested negative.

Despite those negative tests, the patients showed typical COVID-19 symptoms.

The new variant does not yet have a alphanumeric designation. But it's not the first variant that appears able to evade testing. Finnish researchers announced last month that they had identified a strain named Fin-796H with a mutation that made it difficult to detect with some nasal-swab tests, too.

An inability to accurately diagnose infected people could make it harder to curtail the virus's spread at a time when cases across Europe are already spiking.

Confirming infections with the new variant is tricky

The standard molecular lab tests - known as reverse transcription polymerase chain reaction (RT-PCR) tests - hunt for an infection in a swab from a patient's nose, looking for the coronavirus's genetic code.

But according to the French Health Directorate, genetic sequencing revealed that the variant found in Brittany has several mutations on its spike protein that help it evade detection by these diagnostic tests.

Health officials in Brittany eventually confirmed some of the cases caused by the new variant by either testing the patients' blood for antibodies or collecting samples of phlegm the patients coughed up from inside their lungs and running those through a RT-PCR test.

But neither of those methods are the typical COVID-19 tests, which suggests the new variant could be circulating undetected in France and possibly beyond.

However, one European diagnostics company, the Novacyt Group, announced Thursday that its PCR tests can successfully detect the new variant.

The variant doesn't appear to be deadlier or more infectious

All eight of the French patients infected with the new variant died of the virus, according to local outlet LaDepeche, but local health officials said that doesn't necessarily mean it's more deadly than other strains.

There is no evidence yet that the strain is more transmissible than other versions of the virus. More studies are still needed to figure out whether it can evade vaccines or antibodies from prior coronavirus infections, the French health ministry said in a release.

The variant's genetic profile shows it doesn't share any key mutations with B.1.351 and P.1 - the variants first found in South Africa and Brazil, respectively - which are more contagious and can partially evade vaccines.

The variant from Brittany is in the same group of strains as a variant first spotted in Southern California, however. Variants in that group, named Clade 20C, are expected to make up one-fifth of the world's coronavirus infections by April, according to Nextstrain, a genetic repository that tracks the coronavirus's evolution over time.

News of the variant in Brittany came amid France's third peak of infections.

The average number of daily coronavirus cases there has doubled since mid-December, jumping from less than 15,000 to a near record-high of more than 38,000 on Wednesday. The increase prompted Prime Minister Jean Castex to announce new lockdowns for Paris and the surrounding Ile-de-France region on Thursday.

France has been under a nationwide curfew between 6 p.m. and 6 a.m. for the last two months.