Vice President Kamala Harris' PCR test came back negative Monday, following close contact with a staffer who tested positive for COVID-19 on Wednesday, according to a White House official.

The staffer was with Harris throughout the day last Tuesday and tested positive the following morning, Harris' spokeswoman, Symone Sanders, said at the time.

Harris has been tested several times since that close contact, always testing negative, officials said.

-ABC News' Molly Nagle

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. Anthony Fauci strongly recommended against large New Year's Eve parties at Wednesday's White House briefing.

"Should you change or cancel your plans? If your plans are to go to a 40-50 person New Year's Eve party with all the bells and whistles and everybody hugging and kissing and wishing each other a happy new year, I would strongly recommend that this year, we do not do that," Fauci said.

Fauci said "all indications point to a lesser severity of omicron versus delta." But he warned, "we should not become complacent since our hospital system could still be stressed in certain areas."

White House COVID-19 coordinator Jeff Zients said, "We have directly helped more than 30 states and territories by deploying over 2,100 federal personnel and thousands of ambulances, ventilators and other critical supplies."

Supplies include gloves, masks, respirators and face shields, he said.

He added, "More than 13,000 National Guard members have been activated in 48 states to support the COVID response, from vaccinations, to testing, to clinical care."

At the briefing, CDC Director Rochelle Walensky defended the agency's shortened isolation guidelines.

"We do know the vast majority of viral transmission happens in those first five days, somewhere in the 85 to 90% range. So if a person can isolate for the first five days they absolutely should," she said. "We also don't know that antigen tests give a good indication of transmissibility at this stage of infection. On the other hand, we know that after five days people are much less likely to transmit the virus and that masking further reduces that risk. And this is why people need to mask for five days after the five days of isolation."

After five days, asymptomatic people with COVID-19 can leave isolation, but must wear masks around others, according to the new guidelines.

-ABC News' Cheyenne Haslett