A hybrid of the Delta and Omicron coronavirus variants is popping up in several European countries and has made its way into the US, researchers said.

Experts said it is still too early to worry about the new variant, which they said is unlikely to spread easily. 

Two independent cases of the hybrid have been found among the 29,719 positive coronavirus samples sequenced between November and February by scientists from Helix, a lab based in San Mateo, California. The study was published Saturday on medRxiv, the pre-print server for health sciences papers, and has yet to be peer-reviewed.

The hybrid has been dubbed "Deltacron'' by some scientists and has yet to be designated with its own official name. It is a recombinant virus that carries genes from both the Delta and the Omicron variants. 

Other previous studies have identified cases of Deltacron in Europe. Scientists from IHU Mediterranee Infection in Marseille, France, found three patients infected with the hybrid in southern France.  The team's report was published March 8 on medRxiv ahead of peer review. 

In a March 10 update, an international database of viral sequences reported 33 samples of the new variant in France, eight in Denmark, one in Germany and one in the Netherlands, The New York Times reported. 

Experts said it is still too early to worry about the variant, which is unlikely to spread easily and has yet to be designated with its own official name. 

"The fact that there is not that much of it, that even the two cases we saw were different, suggests that it's probably not going to elevate to a variant of concern level" and warrant its own Greek letter name, William Lee, the chief science officer at Helix, told USA Today. 

During a World Health Organization media briefing on March 9, Dr Maria Van Kerkhove, an American infectious disease epidemiologist and the World Health Organizations's COVID-19 technical lead, also acknowledged the variant, saying that there are "very low levels" of the recombinant's detection. 

"This is something that is to be expected, given the large amount of circulation, the intense amount of circulation we saw with both Omicron and Delta," she said.

Van Kerkhove said scientists have yet to see any change in severity with this recombinant, but there are many studies are underway.

"Unfortunately, we do expect to see recombinants, because this is what viruses do, they change over time," she said, adding that the virus is infecting animals, with the possibility of infecting humans again.

"So, again, this pandemic is far from over. We cannot allow this virus to spread at such an intense level," she said.

The variant is extremely rare and hasn't yet displayed the ability to grow exponentially, according to experts interviewed by the Times. 

Dr Etienne Simon-Loriere, a virologist at the Institut Pasteur in Paris, told the Times that the gene that encodes the virus' surface protein, known as spike, is almost completely derived from Omicron. The rest of the genome comes from the Delta variant.

The spike protein is essential when it comes to invading cells. It is the main target of antibodies produced through infections and vaccines. So the antibodies that people developed against Omicron, either through prior infections, vaccines, or both, should work just as well against the new recombinant, according to Simon-Loriere. 

"The surface of the viruses is super similar to Omicron, so the body will recognize it as well as it recognizes Omicron," he said.