Experts Say You Don’t Need to Worry About Deltacron

Researchers in several European countries have recently reported several COVID-19 cases that appear to be genetic hybrid of Delta and Omicron.

The hybrid, a recombination virus that has been dubbed "Deltacron," is not a cause for concern, according to infectious disease experts.

“For some viruses, recombination among different individual viruses or different viral variants is very, very common,” Maciej Boni, MS, PhD, associate professor of biology at Pennsylvania State University’s Center for Infectious Disease Dynamics, told Verywell. “This does not mean that a completely new virus is being produced, nor that the virus will be more dangerous and more transmissible.”

In January, researchers in Cyprus reported COVID-19 viral genomes that featured characteristics of both Omicron and Delta. The media quickly spread the news of a potential "super variant," but the incident was later discovered to be the result of a laboratory mistake.

Two months later, researchers in France reported three COVID-19 cases that appear to be a Delta variant with an Omicron spike protein in an article that has not been peer-reviewed.

In recent weeks, scientists have reported 38 similar cases in France, eight in Denmark, and one each in Germany, the Netherlands, and Belgium, according to the GISAID international database of viral sequences. Helix, a California-based genetic sequencing company, said in a pre-print study that it found two cases of "Deltacron" in the U.S. between mid-January and mid-February.

Despite reports of the variant at least as early as January, it remains rare and hasn’t grown exponentially.

The World Health Organization labeled the AY.4/BA.1 recombinant, as some scientists are calling it, a “variant under monitoring.” Variants in this category have genetic changes which may affect its characteristics, but the epidemiological impact of these changes isn’t yet clear.

Should You Worry About a Recombinant Virus?

Recombination happens when pieces of genetic material are broken up and rejoined in a new arrangement.

In the case of COVID-19, this sometimes happens when multiple viruses infect the same cell. When the virus replicates, an enzyme may stitch together different sections of the genomes together, forming a kind of mosaic virus. This process is common in many virus families, including coronaviruses, enteroviruses, and human immunodeficiency virus (HIV).

In any recombination, it’s difficult to know which characteristics will show up in the final version. In the case of recombinant COVID-19, it’s not usually clear whether the virus will be more transmissible or cause more severe disease based on the genetic sequence.

Boni uses a mule—an animal bred from a donkey and a horse—as an analogy.

“You don't know if a mule is going to have the ears of a donkey and the nose of a horse, or the nose of the donkey and the ear of the horse,” Boni said. “The same goes for viruses. You don't know if it's going to have Omicron’s severity and Delta's transmissibility or the other way around—it's completely unpredictable.”

Since the various reported Delta-Omicron recombinants differ in terms of genetic makeup, lumping them together with the term “Deltacron” doesn’t make sense, Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, told Verywell in an email.

“Which genes are recombined differs in these hybrids but there’s no reason to believe it’s any more transmissible than other variants, and the fact that these recombinants are rare supports that notion,” Adalja said. “Severity is also likely to be no worse than Delta, since Delta is the more severe variant that these hybrids are comprised of.”

Where Current Research Stands

The analysis offered by the French researchers isn’t sufficient to show whether their sequencing of the virus is evidence of a genetic insertion, or if it’s equally explainable by a standard mutation, Boni said.

Still, he said he wouldn’t rule out the possibility that the data shows an instance of recombination. “There are hundreds of thousands of viruses—maybe millions at this point—that have been sequenced, and some of them are recombinants," he said.

At most 5% of circulating COVID cases in the United States and the United Kingdom may be recombinants, according to an analysis by Emory researchers that has not yet been peer reviewed.

Once scientists have identified and isolated a viral recombinant, they can test it in a number of ways. In a lab setting, they can grow it in cell cultures to see how it infects lung cells and other tissues. Infecting lab animals will also give a sense of its relative transmissibility and severity.

Another team of French researchers is already growing and testing new samples of the Delta-Omicron recombinant virus, The New York Times reported.

If the variant catches on and infects several thousand people, scientists can observe differences between the hybrid, Delta, and Omicron in the real world.

How Dangerous Is the Delta-Omicron Hybrid?

Health experts have long touted vaccination as the best protective measure against any COVID-19 variant. The current vaccines induce immunity to the spike protein on the outside of the virus. If the spike protein in the recombinant virus is coded to look like Omicron, a vaccinated individual may have a similar level of protection against the new variant.

It is a “reasonable assumption,” Boni said, that the current vaccines will adequately protect against this recombination, though no conclusions can be reached without more data.

Adalja agreed, saying these recombinants are a mix of variants that many people already have some exposure to, and they are not likely to pose a major risk.  

Ultimately, time will tell. If, in a few months, a Delta-Omicron hybrid appears to be spreading substantially, researchers will do more experiments to better understand how it transmits and promotes disease.

However, “if it turns out in a few months that these new viruses were detected in a few people and then never again, it's just going to disappear,” Boni said.

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