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Chain of transmission between cases as established by epidemiological investigations

A mutant SARS-CoV-2 variant that has appeared in East Asia appears to cause milder infections than the form without this mutation. Overall, there are initial indications that the coronavirus could weaken.

As early as January and February 2020, researchers from Singapore identified a SARS-CoV-2 variant in a cluster of Covid-19 patients that had a 382 base pair deletion. The variant Δ382 lacks a piece of the genome in an area in which the genes ORF7b and ORF8 are located. As a result of the deletion, ORF7b is shortened and the transcriptional regulatory unit is removed from ORF8, whereby the gene is shut down.

To investigate how the deletion affects the properties of the virus, the researchers led by Barnaby Young and Professor Dr. Lisa Ng of the Singapore Immunology Network reviewed the course of patients infected with the mutated variant with those who carried the unmutated virus. None of the 26 patients who wore the Δ382 variant required ventilation, whereas 26 (28 percent) of the 92 wild-type patients. This is what the researchers report in the journal “The Lancet” .

In addition, the patients with the mutated virus had lower levels of pro-inflammatory cytokines and chemokines, which are associated with a severe course of Covid-19. Their T-cell response and the regulation of blood platelets were more effective. The researchers conclude from this that ORF8 could be a good starting point for therapies, but also for the development of virus strains that can be used for conscious infections in the context of human challenge studies. Such strains are currently being worked on .

What these results mean for the pandemic is still unclear. Although the Δ382 variant successfully spread at the beginning of the pandemic, it has not been detected since March. Nevertheless, deletions in ORF8 occurred several times independently of one another, the researchers report. The gene appears to be a mutation hotspot that is important for adaptation to humans. Studies have shown that ORF8 is highly immunogenic and antibodies to the viral protein appear early in the infection. The SARS coronavirus-1, which was responsible for the SARS epidemic in 2002/2003, had also acquired a deletion in ORF8. Their effect on the epidemic at the time is unclear, the researchers write.

The consequences of mutations in SARS-CoV-2 , reported Professor Dr. Christian Drosten from the Berlin Charité already in March on the NDR podcast . Coronaviruses mutated, according to the virologist. This does not happen quickly, but mutations still occur time and again – also with SARS-CoV-2. “We can rely on the virus to mutate,” said Drosten. It is also certain that the virus will take on new properties.

That doesn’t have to cause concern. Most mutations are harmful to the virus and are being eradicated by competing virus strains. Under competitive pressure, a selection would always be made for better transferability, not for a higher death rate for the host, as this is a hindrance to spread.

As a rule, a new virus adapts to its host over time. According to Drosten, one possibility is that the virus is starting to affect the nasal lining more and less the lungs. Over time, this would turn the lung disease into a kind of runny nose. The pathogen could therefore become less dangerous if it adapts to humans.

The death rate is falling

There are already initial indications that this could actually happen. The death rate among Covid 19 patients is falling in some countries, for example in the USA and Germany. On the one hand, this may be due to the falling average age of the patients. This is the Robert Koch Institute (RKI) according to data dropped after an increase of initially 42 to 52 years in April now at 32 years. At the same time, the proportion of patients who had to be treated in hospital fell from 22 percent in April to 6 percent. The death rate of Covid-19 patients fell from 7 to 0.1 percent over the same period. In young people, the corona infection is usually milder.

On the other hand, in addition to the young age of the patients, the milder courses could also be due to weakened virus variants. But they still have to be found. Another mutated variant has established itself more strongly than the Δ382 variant: D614G is now the dominant strain of SARS-CoV-2 worldwide . But whether it is more infectious than other strains and how it affects the severity of the disease remains to be investigated.

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