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At the beginning of January it was still a laboratory error, but now there are actually cases in which a recombination of the delta and omicron variants of the coronavirus has been detected.
At the request of SPIEGEL, the Robert Koch Institute (RKI) confirmed that there had been a confirmed infection with the "Deltakron" recombinant in Germany.
Such cases have previously been reported in France, the Netherlands, Great Britain and Denmark.
In January, the mixed variant of delta and omicron was supposed to have appeared on Cyprus.
But afterwards it turned out that it was a false alarm: apparently laboratory samples had been contaminated.
This time, however, it really seems to be a recombination variant.
Answers to the most important questions at a glance:
What is Deltakron?
Deltakron is a so-called recombination variant or hybrid variant from the corona variants Delta and Omikron.
The omicron variant currently predominates worldwide, which is more infectious than previous variants, but is somewhat milder in vaccinated people.
Previously, the Delta variant was dominant in Europe.
It is considered to be more aggressive and causes more severe courses, especially in people at risk.
The genome database "Gisaid" announced last week that the Institut Pasteur in France has shared clear evidence on the platform for the first time that proves a recombination of delta and omicron.
The analysis provides unequivocal confirmation of the structure of a recombinant virus derived from the Delta AY.4 and Omicron BA.1 lines, according to a statement on the Gisaid website.
The recombined virus has been circulating in several French regions since the beginning of January.
Genomes with a similar profile have also been reported in Denmark and the Netherlands.
Further studies are necessary to clarify the origin of the recombination variant and to find out whether it is the same recombination in each case.
A French research team that has already published a preprint for Deltakron (the variant is called "Deltamicron" in the study) assumes that the hybrid variant contains characteristic mutations of both lines.
It consists of an almost complete spike gene from omicron within a delta lineage, write the authors of the work, which has not yet been peer-reviewed.
The scientists examined the samples from three French patients using genome sequence analysis.
According to the study, the recombinant could possibly bind to the host cell a little better.
How does a recombination variant arise?
Recombination variants are common in coronaviruses.
Although it is relatively rare, some people contract two types of coronavirus at the same time.
Especially in the period between December and January, when the Omicron variant was just replacing the Delta variant in Europe, there was a high probability of coming into contact with both variants.
It is possible for two virus types to invade the same cell at the same time.
Then, when the virus starts to multiply, the genetic material can mix and produce a recombination of both variants.
In most cases, however, such a hybrid variant does not continue to exist because it has no evolutionary advantage compared to the two original variants.
However, in some cases, the newly created variant could prevail or coexist with the original variants.
How dangerous is Deltakron?
Certainly the biggest concern is that deltakron is as contagious as omicron and as pathogenic as delta.
So far there are only very few known cases of Deltakron, at the same time the recombinant has been in circulation since the beginning of January.
At first glance, this does not suggest that it will spread even faster than Omicron and that it could soon become established.
Nevertheless, it is too early to make clear statements about the dangers of Deltakron.
"The fears have been around for a long time," Etienne Simon-Loriere of the French Institut Pasteur told the New York Times.
So far, the recombinant is still extremely rare and shows no signs of exponential growth.
Deltakron's genome does not indicate that a new phase of the pandemic is entering either: the spike protein, with which the coronavirus docks to human cells, comes mainly from omicron;
the rest of the genome of Delta.
According to Simon-Loriere, immune protection that has already been built up against omicron - for example through vaccination or infection - should also work against Deltakron.
"The surface of the virus is very similar to the surface of omicron, so the body will recognize it the same way it recognizes the omicron variant," Simon-Loriere said.
However, the omicron variant is an immune escape variant that can partially bypass immune protection.
This means that a previous infection or a vaccination does not protect quite as well against an infection with Omikron.
However, a triple vaccination protects very well against severe courses and hospital stays.
The vaccines were developed against the so-called wild type of the corona virus, but they are also very effective against the delta variant.
If the new recombinant now contains components from Delta, the vaccines could possibly provide even better protection than with Omikron.
What does this mean for the further course of the pandemic?
In the UK, Deltakron has apparently been discovered more than 30 times, as the Guardian reports.
According to the Reuters news agency, at least 17 cases have also occurred in the United States.
It is unclear whether these are exactly the same recombinants in each case.
Also what it means for the further course of the pandemic.
If the hybrid variant is more contagious than the omicron variant, it could prevail as the pandemic progresses - especially if further measures are relaxed and incidences continue to rise.
If Deltakron causes more severe courses than Omikron, more people would come to the hospital or intensive care unit than is currently the case.
The number of deaths would also rise again.
Researchers such as Christian Drosten have already mentioned such a scenario as a possibility.
WHO epidemiologist Maria van Kerkhove tweeted last week that recombination variants are to be expected when two corona variants such as delta and omicron are circulating so strongly.
The World Health Organization is monitoring and discussing this.
Nevertheless, experts are not overly concerned.
Because Deltakron is not the first recombination variant of Sars-CoV-2.
"This happens whenever we're in the transition phase from one dominant variant to another," Jeffrey Barrett, the former head of the UK's Wellcome Trust Sanger Institute's Covid-19 Genome Initiative, told The Guardian.
"It's not much more than a scientific curiosity." So far, there have been very few Deltakron cases worldwide, and it doesn't look like there's anything to worry about.
"We need to keep an eye on the behavior of this recombinant," Lawrence Young, a virologist at the University of Warwick, told The Guardian.
You have to monitor the infectiousness and the ability to bypass the vaccine protection.
Deltakron shows »how important it is to sequence and monitor gene samples.
As the virus continues to circulate, especially in an undervaccinated population, we will see more and more variants of the virus.”
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