Health officials are closely monitoring a new hybrid coronavirus variant that contains elements of both the delta and omicron variants—but experts believe it is "probably not going to elevate to a variant of concern level."

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What is 'deltacron'?

In February, Scott Nguyen, a scientist with the Public Health Laboratory in Washington, D.C., was analyzing coronavirus samples from the Global Initiative on Sharing Avian Influenza Data (GISAID) when he identified several samples that contained elements of the omicron and delta variants. Initially, these cases were believed to be a coinfection of both variants—but Nguyen suspected that the samples were actually a recombinant virus.

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Typically, "recombinants arise when more than one variant infects and replicates in the same person, in the same cells," said Lawrence Young, a virologist at the University of Warwick.

When Nguyen searched for the same pattern of mutations in GISAID, he identified more possible recombinants across the Netherlands and Denmark. "That led me to suspect that these might be real," he said.

"That day, we rushed to double-check what he suspected," said Etienne Simon-Loriere, a virologist at the Institut Pasteur in Paris. "And, yeah, we quickly confirmed that it was the case."

"Deltacron is a product of both the delta and omicron variants circulating in the same population," Young said.

Currently, some scientists are referring to the new hybrid as the AY.4/BA.1 recombinant, and others have given the variant nicknames like "deltamicron" or "deltacron."

Where has 'deltacron' been found?

Since its identification, Simon-Loriere and his colleagues have identified more samples of the recombinant virus. On March 8, the researchers added the first genome of the AY.4/BA.1 recombinant on GISAID.

As of March 10, there were 33 samples of the new variant identified in France, eight in Denmark, one in Germany, and one in the Netherlands, the New York Times reports.

According to the UK Health Security Agency (UKHSA), around 30 cases have been detected in the United Kingdom.

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In addition, genetic sequencing company Helix identified two cases in the United States. To identify more U.S. cases, Nguyen and his colleagues are also analyzing additional database sequences from the United States.

Notably, Simon-Loriere said there could be several different recombinant viruses that stem from delta and omicron.

"The one we see in France and in Denmark/Netherlands look super similar and might be the same recombinant [with the same parental viruses] that have travelled," Simon-Loriere said. However, the possible delta-omicron recombinants reported in the United States and United Kingdom seemingly combine different pieces of their parental viruses. As a result, they differ from the cases seen in France.

"We might need to find a different name to indicate these recombinant, or start adding a number," Simon-Loriere added.

Why you don't need to be worried about 'deltacron'

Notably, experts have emphasized that recombinant variants are somewhat common, which means that deltacron is not the first and will likely not be the last to occur for the coronavirus.

"This happens whenever we are in the switchover period from one dominant variant to another, and is usually a scientific curiosity but not much more than that," said Jeffrey Barrett, who formerly led the Covid-19 genomics initiative at the Wellcome Trust Sanger Institute.

According to William Lee, chief science officer at Helix, "[t]he 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," or have its own Greek letter name.  

Currently, in the places where deltacron has been detected, "there are very low levels of this detection," said Maria Van Kerkhove, an American infectious disease epidemiologist and the World Health Organization's (WHO) Covid-19 technical lead.

For now, WHO has not seen "any change in the epidemiology," Van Kerkhove said. With deltacron, "we haven't seen any change in severity. But there are many studies that are underway," she added.

Ultimately, "[i]t's only a variant if it produces a large number of cases," said William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health. "So no, if it's not causing lots of cases, people don't need to be concerned." (Snider, USA Today, 3/10; Davis, The Guardian, 3/11; Zimmer, New York Times, 3/11; Lin II/Money, Los Angeles Times, 3/11)