What is Deltacron?

As the portmanteau suggests, Deltacron is a Covid variant that contains elements of Delta and Omicron – in other words, it contains genes from both variants, making it what is known as a recombinant virus.

“These recombinants arise when more than one variant infects and replicates in the same person, in the same cells,” says Prof Lawrence Young, a virologist at the University of Warwick. “Deltacron is a product of both the Delta and Omicron variants circulating in the same population.”

This week, Gisaid, a global community of scientists that shares virus information, posted that the first solid evidence for this variant had been shared by the Pasteur Institute in France.

Where has this variant been found?

Gisaid says the variant has been identified in several regions of France and appears to have been circulating since the start of the year. “Genomes with a similar profile have been also identified in Denmark and the Netherlands,” Gisaid says.

There have also been reports of Deltacron being detected in the US, and about 30 cases have been detected in the UK, according to the UK Health Security Agency (UKHSA). The i newspaper said the first cases of person-to-person transmission of Deltacron in the UK were expected to be confirmed this week.

Dr Etienne Simon-Loriere of the Institut Pasteur cautioned that there could be several different recombinant viruses formed 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,” he said. But, he added, the possible Delta-Omicron recombinants reported in countries including the UK and US appear to combine different pieces of their parental viruses, and therefore differ to the Deltacron seen in France.

“We might need to find a different name to indicate these recombinant, or start adding a number,” he said.

How worried should we be?

Experts have been quick to stress that recombinant variants are not uncommon, and that Deltacron is not the first and will not be the last to occur for Covid.

“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,” says Dr Jeffrey Barrett, who formerly led the Covid-19 genomics initiative at the Wellcome Trust Sanger Institute.

With only a small number of cases of Deltacron so far identified, however, there is not yet enough data about the severity of the variant or how well vaccines protect against it.

Soumya Swaminathan, the chief scientist at the World Health Organization, tweeted on Tuesday: “We have known that recombinant events can occur, in humans or animals, with multiple circulating variants of #SarsCoV2. Need to wait for experiments to determine the properties of this virus. Importance of sequencing, analytics and rapid data sharing as we deal with this pandemic.”

Young agrees. “We need to keep an eye on the behaviour of this recombinant in terms of its transmissibility and its ability to escape vaccine-induced immune protection,” he says. “This also serves to reinforce the need to maintain genetic surveillance. As the virus continues to circulate, particularly in under-vaccinated populations and in people whose vaccine-induced immunity is decaying, we are very likely to see more variants including those generated through recombination.”

But that does not mean the variant is a reason to panic: according to the UKHSA, the variant is not exhibiting a growth rate of concern.

“It has been seen in the UK a small number of times, and so far seems to be very rare anywhere in the world, with only a few dozen sequences among the millions of Omicrons,” says Barrett. “So I don’t think it’s anything to be concerned about at present, though I’m sure it will continue to be monitored.”

Previous waves of Delta and Omicron, as well as vaccinations, mean there is likely to be at least some protection against this variant.