OMICRON VARIANT: More contagious, less severe than Delta?

There are new clues as to why the Omicron variant may produce milder COVID-19 symptoms, despite being more transmissible.

Several recent studies that looked at the effect of the virus on mice and hamsters have found that the Omicron variant leads to a lower viral load in the lungs and less damage to the tissues compared to previous variants.

One study from Belgian researchers published online looked at how Omicron infected Syrian hamsters.

The researchers found that the hamsters with Omicron had a 99.9 per cent lower viral load in the lungs compared to hamsters infected with older strains of the virus.

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Syrian hamsters have been considered an important tool for COVID-19 research, as these animals are known to be highly susceptible to getting seriously ill from the virus.

A similar study looking at Syrian hamsters and led by British researchers was also released on Dec. 26. The researchers compared 11 hamsters infected with the Omicron variant to six infected with previous variants, including Delta.

They found that Omicron-infected hamsters had fewer signs of weight loss, ruffled fur and breathing difficulties — all of which are clinical signs of COVID-19 in Syrian hamsters.

“Further investigation is required to conclusively determine whether Omicron is less pathogenic in Syrian hamsters and whether this is predictive of pathogenicity in humans.”

A third study that looked at both mice and Syrian hamsters was published by U.S. and Japanese researchers on Dec. 29. Once again, the researchers found that rodents with Omicron had less weight loss and a lower viral load in their respiratory tracts.

The Omicron-infected rodents also had less damage to the lung tissues, suggesting that the variant can’t replicate as well in the lungs.

Another U.K.-led study published on Dec. 30 looked at the effect of Omicron on mice. Much like the studies that looked at hamsters, the researchers found that the mice infected with Omicron lost less weight and had better signs of recovery compared to mice that had the Delta variant and other older strains.

Oral swabs were also taken from all of the mice two, four and six days after infection. The viral loads in the lower and upper respiratory tract were found to be 100-fold lower in the mice with Omicron.

“Our results, and emerging from human observational studies, suggest that the Omicron variant may lead to less severe and/or more rapid recovery from clinical disease reflected in reduced hospitalization,” the authors wrote.

However, the researchers warned that the high transmissibility of the new variant could still inundate hospitals, despite evidence of milder symptoms.

“The higher transmissibility could still place huge burden upon health care systems even if a lower proportion of infected patients are hospitalized,” they wrote.

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