So-called “Delta-cron” hybrid variant identified for the first time

Scientists have confirmed the existence of a new COVID-19 variant that combines mutations from both omicron and delta variants for the first time, and there are reported cases in both Europe and the U.S.

This so-called Delta-cron COVID variant appears to have been identified in the U.S. by a California lab, according to a new study published to research site medRxiv.

What is recombination?

Between November 2021 and February 2022, SARS-CoV-2 Delta and Omicron variants co-circulated in the United States, allowing for co-infections and possible recombination events.

An article by Livescience recalled how the variant arose.

“The hybrid variant arose through a process called recombination — when two variants of a virus infect a patient simultaneously, exchanging genetic material to create a new offspring. Scientists say that the “backbone” of the deltacron variant comes from the delta variant, while its spike protein — which enables the virus to enter host cells — derives from omicron, according to the medRxiv paper.”

The abstract of this study published on the medRxiv site stated that “We sequenced 29,719 positive samples during this period and analyzed the presence and fraction of reads supporting mutations specific to either the Delta or Omicron variant. 

“Our sequencing protocol uses hybridization capture and is thus less subject to artifacts observed in amplicon-based approaches that may lead to spurious signals for recombinants. We identified 20 co-infections, one of which displayed evidence of a low recombinant viral population. 

“We also identified two independent cases of infection by a Delta-Omicron recombinant virus, where 100% of the viral RNA came from one clonal recombinant.”

What are the implications of this Delta-Omicron recombinant variant?

The Delta-cron hybrids or recombinants are rare, according to the study, which added that there is no evidence such mutations spread more easily than the highly transmissible Omicron. 

Dr. Soumya Swaminathan, the chief scientist at the World Health Organization (WHO), has  tweeted about this study, indicating that we “need to wait for experiments to determine the properties of this virus.”


World Health Organization COVID-19 technical lead Dr. Maria Van Kerkhove, an infectious disease epidemiologist, also addressed the variant at a media briefing, acknowledging the existence of the blend of Delta, also known as AY.4, and Omicron, also known as BA.1.

“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.

“This is what viruses do. They change over time.”

NOTE: “Deltacron” is a media portmanteau. Scientists have not yet officially named the variant. Neither the World Health Organization nor the CDC has named it a variant of concern.

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