COVID updates: Secretary of Defense Lloyd Austin tests positive

Last week, the CDC reported that omicron had overtaken delta to become the dominant COVID-19 variant in the U.S. However, on Tuesday, the CDC revised its initial estimates to noticeably lower numbers of omicron cases. 

Last Monday, the CDC said omicron was estimated to makeup more than 73.2% of new cases as of Dec. 18. Now, the CDC says just 22.5% of new U.S. cases were estimated to be omicron as of Dec. 18. 

According to new data from this week, the CDC says omicron is now estimated to account for 58.6% of all new cases, officially making it the dominant strain in the U.S. In the New York and New Jersey region as well as the deep South, omicron is estimated to account for more than 85% of new cases. 

A CDC spokeswoman said in a statement, "There was a wide predictive interval posted in last week’s chart, in part because of the speed at which omicron was increasing. We had more data come in from that timeframe and there was a reduced proportion of omicron. It’s important to note that we’re still seeing steady increase in the proportion of omicron." 

ABC contributor Dr. John Brownstein, an epidemiologist at Boston Children's Hospital, said, "It may be possible that a large portion of their [the CDC's] sequencing data had come from labs that were specifically looking for s-gene samples, thus falsely elevating the percent omicron in samples." 

-ABC News' Arielle Mitropoulos

When New York City students return to school after winter break, they will see PCR testing doubling in every school, Mayor Bill de Blasio announced Tuesday.

Testing will include both vaccinated and unvaccinated students, he said, and teachers and staff will also be able to test.

If a positive case is detected, all students in that class will be given a rapid at-home test. If they are asymptomatic and test negative, they can return the day after their first negative test. Students will then be given a second at-home test within seven days of exposure.

That shifts from the previous plan of sending entire classrooms home to learn online when one or more students test positive.

Schools will still be closed if evidence of major in-school spread.

The city's Department of Education staff is at a 96% vaccination rate, officials said.

-ABC News' Alexandra Faul, Aaron Katersky

The Broadway musical Ain't Too Proud will ends its run on Jan. 16, 2022. The show has been closed since Dec. 15 due to COVID-19 cases and hopes to resume Tuesday night for its final few weeks, ABC New York station WABC reported.

The musicals Jagged Little Pill and Waitress as well as the play Thoughts of a Colored Man have also announced that that they're closing for good amid the rise in cases.

Dr. Ashish Jha, dean of the Brown University School of Public Health, said he agrees with the CDC's ruling to shorten isolation time from 10 days to five days for asymptomatic people with COVID-19. That must be followed by five days of mask wearing around others.

Jha told "Good Morning America" on Tuesday that five days is enough to stop the spread for asymptomatic people because most people are contagious in the couple days before they have symptoms and in the two to three days symptoms begin.

But Jha said he think it would "make a big difference" if the CDC required COVID-19 patients to get a negative test before leaving isolation.

"I don’t know why the CDC did not put that in -- I suspect it might be because tests are still hard to come by," he said.