Why is the SARS-CoV-2 Omicron variant milder?

The single point mutation T9I in the envelope protein of the SARS-CoV-2 Omicron variant changes channel properties and attenuates virus production and virulence

In November 2021, a new SARS-CoV-2 variant emerged in South Africa and was designated the fifth variant of concern and named Omicron. It was detected in more than 26 countries worldwide, including China. The Omicron variant is highly transmissible and has extensive morbidity, which has raised concerns related to antiviral therapy. Recent reports have revealed that the Omicron variant exhibits a longer cycle of viral shedding and a decreased replication capacity and results in substantially attenuated lung pathology, indicating that the pathogenic ability of the Omicron variant is lower than that of previous variants.