Notably, loss of smell appears to be less common after infection with omikron BA.1
The omikron BA.1 variant of the coronavirus is less able to penetrate the brain and causes less inflammation in brain cells than the virus variant from the first corona wave. This is the result of research with hamsters and human brain cells by scientists at Erasmus MC. ‘Good news, but no guarantee for the future.’
Loss of smell, concentration problems and brain fog: infection with the coronavirus can cause all kinds of problems with the brain. But there are differences between the virus variants. Notably, loss of smell appears to be less common after infection with omikron BA.1.
Scientists from the Viroscience and Psychiatry departments of Erasmus MC have now shown that the omikron BA.1 and delta variants penetrate the brain less well than the first wave coronavirus variant, called D614G. They publish their research in Acta Neuropathologica Communications.
The researchers infected groups of four hamsters with the three virus variants. After five days, they looked at whether and how much virus was present in the nose, the olfactory center and other parts of the brain. Previous research has shown that the coronavirus can enter the brain via the olfactory nerve. The researchers used hamsters because a coronavirus infection in them is similar to that in humans.
In the hamsters infected with the omikron BA.1 or delta variant, virus was found in the nose, but no infected cells were found in the brain. According to the researchers, this suggests that the virus is unable to enter the brain through the olfactory nerve.
This was the case with the D614G virus variant, and the scientists saw an inflammatory response in the olfactory center of the hamsters’ brains. This may partly explain the loss of smell in patients. No virus or inflammatory response was found in other parts of the brain.
Human brain cells
The researchers saw the same differences in human brain cells made from induced pluripotent stem cells. Omikron BA.1 and delta were less able to infect the brain cells and induce an inflammatory response than the D614G variant.
Where do the differences come from? According to the researchers, they are probably the result of the same mutations that make new virus variants less pathogenic. ‘All viruses evolve over time and that means different properties. In this case it seems good news for the effect on the brain, but I can’t give any guarantees for future virus variants. The evolution of this virus remains difficult to predict,’ says research leader and virologist Dr Debby van Riel.
It is not clear from this study what infection with the coronavirus does to the brain in the longer term. ‘We looked at the first five days after infection, but we also want to know what happens in the long term. For example, how long does the inflammatory reaction last and can that explain the neurological complaints of people with lung covid? We would like to find out’, says virologist and researcher Dr Lisa Bauer.
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