Symptoms of milder Omicron variant, pulmonary remission in rodents: study

TORONTO – There are new clues as to why the Omicron variant may produce milder, albeit more virulent, COVID-19 symptoms.

Several recent studies looking at the effects of viruses on mice and hamsters have found that the Omicron variant resulted in lower levels of the virus in the lungs and less damage to tissues than the Omicron variant. earlier form of SARS-CoV-2.

All of these rodent studies are preprint, which means they have yet to be peer-reviewed or published in a medical journal.

A study from Belgian researchers published online on Gifting Day looked at how Omicron infects Syrian hamsters. The researchers found that hamsters infected with Omicron had a 99.9% lower viral load in their lungs than guinea pigs infected with older strains of the virus.

The Syrian hamster has been considered an important tool for COVID-19 research, as these animals are known to be highly susceptible to severe illness from the virus.

A similar study of Syrian hamsters led by British researchers was also published on December 26. The researchers compared 11 guinea pigs infected with the Omicron variant with six infected with the Omicron variant. infected with earlier variants, including Delta.

They found that hamsters infected with Omicron showed less signs of weight loss, ruffled fur, and difficulty breathing – all clinical signs of COVID-19 in Syrian guinea pigs.

“Further investigation is needed to clearly determine whether Omicron is less pathogenic in Syrian hamsters and whether this is predictive of human pathogenicity,” the authors write.

A third study looking at both Syrian rats and hamsters was published on December 29 by US and Japanese researchers. Again, the researchers found that the rodents had reduced Omicrons. They weigh less and have a lower amount of virus in their airways.

The Omicron-infected rodents also suffered less damage to lung tissues, suggesting that this variant could not replicate as well in the lungs.

Another UK-led study published on December 30 looked at the effects of Omicron in mice. Like the studies on hamsters, the researchers found that the mice infected with Omicron lost less weight and showed better signs of recovery than mice with the Delta variant and other older strains.

Oral swabs were also obtained from all mice two, four and six days after infection. Viral loads in the lower and upper respiratory tract were 100-fold lower in mice given Omicron.

“Our results, and emerging from observational studies in humans, suggest that the Omicron variant may lead to less severe and/or faster recovery from clinical illness,” the authors write. reflected in the reduction in hospitalization rates”.

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

“Higher transmissibility could still place a heavy burden on health care systems even at a lower proportion of infected patients requiring hospitalization,” they wrote.


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