Mankind has already had to endure numerous variants of Sars-CoV-2. With Omicron, an extremely contagious one seems to have prevailed, which is also considered less dangerous. But is that even true? Researchers make the direct comparison.
In November 2021, the discovery of a new variant of Sars-CoV-2 in South Africa caused uncertainty worldwide: it had an unusually large number of mutations. Experts fear that it could be highly contagious and possibly penetrate the protective shield of the vaccine more easily. But something else becomes apparent after a few days. Omicron, as it is called, seems less likely to cause illness. But skepticism remains, because other variants such as Alpha, Delta and Gamma had already left a deadly impression.
But with the worldwide spread of Omikron, the hope for a “mild variant” seemed to be confirmed. But can you really say that exactly? An international research team has taken on the question and compared the dangerousness of variants. Their study, which was published in the journal “Nature Communications”, confirms: Omicron is the least pathogenic variant of Sars-CoV-2 to date. In this context, experts speak of the “degree of pathogenicity” of a virus.
For their study, the researchers examined hamsters that had been in contact with different variants. “When the omicron variant was just emerging in South Africa, we had the opportunity to study animals that had already been infected with the omicron, gamma, delta or an original corona variant in another study,” says Georg Beythien from the University of Veterinary Medicine Hannover (TiHo), one of the authors of the study, according to a statement from his university.
The team examined how infection with the different variants affected the tissues in the nose, trachea, bronchi and lungs – in combination with the viral load and the response of the immune system. “The damage was less in all animals infected with the omicron variant than in those infected with earlier variants of the virus,” says lead author Federico Armando. The viral load in the examined tissues was also lower in omicron-infected animals than in the other groups.
“We examined all sections of the upper and lower airways – from the nose to the lungs,” says study leader Malgorzata Ciurkiewicz. Many previous studies have focused on the lungs to understand how the severe to fatal courses of Covid-19 come about. “But we also see clear differences between the variants in the nasal mucosa. This may explain the less frequent occurrence of loss of smell after an omicron infection,” says Ciurkiewicz.
The alveoli of the lungs in hamsters were remarkably little affected by the omicron infection, which corresponds well with the lower number of severe courses of pneumonia in omicron-infected people. Ciurkiewicz suspects that the reason for this lies in the way the virus enters the cells. “We observe that the omicron variant prefers to use a different mechanism than previous variants. It is probably not as efficient for the alveoli cells.”
And the researchers also draw their conclusions from the low pathogenicity of omicron: “The virus seems to have adapted further to humans as a new host,” explains Wolfgang Baumgärtner, Director of the Institute of Pathology at the TiHo, who is leading the study together with Ciurkiewicz Has. “It does less damage to him to spread more efficiently.”
However, the question remains as to why the omicron variant, despite its lower pathogenicity – and apparently lower viral loads in the respiratory tract – has spread among humans much faster than previous variants. Various explanations are discussed in the study: the omicron variant could be more stable on surfaces than other variants. But the rarer loss of smell in humans could also play a role – as a result, there may have been a larger number of undiscovered cases that contributed to the spread, according to the researchers.
“The greater spread of omicrons was probably also favored by the fact that the variant has changed structurally and is therefore better able to escape the immune system,” adds Ciurkiewicz. “As a result, vaccination or a previous infection does not protect us as well against omicron as against earlier variants.” However, other biological and societal aspects would have to be taken into account in order to understand the spread, the communication goes on to say. In order to clarify the connections between pathogenicity and transmissibility on a biological level, further studies are therefore necessary.
