pandemic
Deltrakron – What’s to come with mixed variants
A biological-technical assistant prepares PCR tests for the coronavirus. Photo: Julian Stratenschulte/dpa
© dpa-infocom GmbH
Crossbreeds from the Corona variants Delta and Omikron are sometimes unofficially called Deltakron. Such variants have already been found in several countries. What it’s all about.
As pathogenic as delta, as contagious as omicron – the specter of such a super variant of the corona virus has been haunting for some time. In this context, the catchy but unofficial name Deltakron sometimes appears.
At the beginning of the year, researchers from Cyprus initially wanted to have demonstrated a combination of the two Sars-CoV-2 variants Delta and Omicron. It quickly became apparent that it was most likely an error due to contamination in the laboratory. In the meantime, however, reports of Deltakron cases are piling up again. Questions and answers about this:
What does the WHO say?
The World Health Organization (WHO) is observing a so-called recombinant consisting of one subtype each of delta (AY.4) and omicron (BA.1). The technical abbreviation for this is XD. First samples come from France and are from January. For Germany, the Robert Koch Institute (RKI) speaks of a confirmed case on request and refers to further descriptions in France, Denmark and the Netherlands.
The WHO said there were no signs of good propagation so far. Monitoring by the WHO does not mean that XD is classified as of concern or interest. As a result, it has not yet been given its own name. The term Deltakron, which is sometimes common in the media, is expressly not used by the WHO.
What speaks against the name Deltakron?
For experts, the term is very imprecise and only suitable for illustration. Because it was recently used not only for XD, but for different mixed forms of delta and omicron. It is “not a helpful term, since it is unclear which recombinant is meant and the term conveys an alarmism for which there is no good reason,” said Richard, head of the research group Evolution of Viruses and Bacteria at the Biozentrum of the University of Basel closer.
British virologist Tom Peacock recently clarified on Twitter that the hybrid XD discovered in France is distinct from the one described in the UK, called XF. Neher explained that XD is the only variant in which the omicron spike protein is “more or less perfectly” inserted into a delta genome. The virus enters human cells with the spike protein.
How do such mixed forms arise?
The phenomenon is by no means surprising. “It was foreseeable that there would be such recombinants of Sars-CoV-2. This can always happen when two variants are circulating at the same time: If a person is infected, for example, with delta and omicron at the same time, there can be an exchange of viral genetic material in a doubly infected host cell,” said the virologist Friedemann Weber (Justus Liebig University To water). But that is considered relatively rare. According to experts, in addition to mixed forms from delta and omicron, those from the omicron subtypes BA.1 and BA.2 have also appeared.
The current evidence also has to do with the fact that the virus has changed more and more as the number of infections has increased. In the genetically very similar variants from the first phase of the pandemic, it was difficult to detect recombinations, French researchers write in a preprint on cases in southern France.
Does mixed variety threaten to make the pandemic worse?
“It would be wrong to assume that such recombinants are necessarily horror variants that combine the worst properties of the original variants,” said Weber. The omicron subtype BA.2, which is currently predominant in Germany, is almost as contagious as measles – the virus can hardly grow much more. “Although omicron is often associated with a milder course of the disease, it remains to be seen to what extent this also applies to older unvaccinated people.” Virologist Peacock wrote that of the recombinants seen so far, only XD is perhaps a little more worrying. If any of these mixed forms should behave differently than their original variants, it could be XD.
What has to be done now?
“In some cases, such recombinants have only appeared in limited outbreaks. Others appear to be increasing linearly at the moment, however
fortunately not yet exponential. This has to be observed and taken seriously,” summarized the virologist Christian Drosten in a “Zeit” interview on Wednesday. Weber also advises further observation – he reminded that some variants had already appeared in the pandemic, which were then never heard from again. “These recombinants could also disappear again in the mists of history.”
How well are variants monitored given the current high number of cases?
In Germany, a complete genetic analysis is only carried out and paid for by the laboratories for a very small proportion of all positive findings. At full capacity, the laboratories even sequenced less than five percent of the samples for capacity reasons, said virologist Sandra Ciesek from the University Hospital in Frankfurt. Rare virus variants would only be discovered by chance. She also regrets that the variant-specific PCR has been deleted with the recently amended test regulation: The procedure can be used to detect abnormalities, which have already led to the discovery of some rarer virus variants.