Scientists in the US have found that omicron could be far less damaging to the lungs than previous variants of the coronavirus.
A report in the British scientific journal Nature provides a possible explanation for why omicron appears to cause milder disease.
It cites experiments by virologists at Washington University in St Louis, Missouri, which showed hamsters and mice infected with omicron had viral loads in their lungs at least 10 times lower than those infected with other variants.
Other research teams have also found lower levels of virus in the lungs due to omicron.
One found that omicron could have trouble binding to a protein which protrudes from the surface of many lung cells but is absent from nose and throat cells.
The Nature article points out that rising levels of immunity due to infection and vaccination make it difficult to know whether omicron is intrinsically milder than delta and other previous strains.
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It also notes that, though omicron could be less dangerous, its high transmission rate threatens to overwhelm hospital systems around the world.
University of Cambridge virologist Ravindra Gupta told Nature that omicron could have difficulty penetrating lung cells but linger in the upper airways, where it was more easily expelled from the nose and mouth and, therefore, more infectious.
NSW reported 34,994 positive tests on Thursday and now has 207,000 official active cases, though epidemiologists say the true infection rate is likely to be far higher.
The state had 1609 COVID patients in hospital, 118 more than on the previous day, 131 in intensive care and 38 requiring ventilation.
Six more people died after testing positive for the coronavirus.