Jan 4 (Reuters) - The Omicron variant was estimated to be 95.4% of the coronavirus strains circulating in the United States as of Jan. 1, the U.S. Centers for Disease Control and Prevention (CDC) said on Tuesday. The variant has swiftly spread across the country since its detection on Dec. 1, replacing Delta as the dominant strain and sparking a new wave of infections that pushed daily cases near the 1 million mark on Monday. The CDC said the variant accounted for an estimated 77% of cases in the week ended Dec. 25, up from the 58.6% projection it had disclosed last week. The fast-spreading variant was first detected in southern Africa and Hong Kong in November and has since swept through the globe at lightning speed, although signs that it may cause milder symptoms than previous strains have offered some relief. The CDC had last week lowered its estimate for cases Omicron accounted for in the week ended Dec. 18 to 22% from 73%, citing additional data and discrepancies caused by the variant"s rapid spread. read more The Delta variant accounts for 4.6% of all U.S. COVID-19 cases as of Jan. 1, the CDC data showed.