(NewsNation Now) — The omicron variant of COVID-19 has become the most dominant strain in the United States, health officials said. The Centers for Disease Control and Prevention says it accounts for 73% of all cases across the country.

Omicron is responsible for an estimated 90% or more of new infections in the New York area, the Southeast, the industrial Midwest and the Pacific Northwest. The national rate suggests that more than 650,000 omicron infections occurred in the U.S. last week.

Lines for COVID-19 tests wrapped around the block in New York, Washington and other cities over the weekend as people clamored to find out if they were infected before celebrating the holidays with family.

With the rapid rise in infections, Washington Mayor Muriel Bowser on Monday reinstated an indoor mask mandate until the end of January and required government workers to get vaccinated, including a booster shot.

Boston Mayor Michelle Wu will now require proof of vaccination for indoor dining, indoor fitness venues, and indoor entertainment and recreation establishments starting Jan. 15.

Ohio’s rolling 7-day average of positive cases is higher than it’s been all year. Gov. Mike DeWine says nine out of 10 COVID patients in the state’s hospitals are unvaccinated.

Breakthrough infections are rising among 61% of the country’s fully vaccinated population, including the 30% who have gotten booster shots.

Early data suggests that omicron is doubling its spread every two to three days. The CDC says it took the delta variant about 11 days to do that.