All international travelers to the UK ages 12 and up must show proof of a negative COVID-19 test taken within two days of departure, officials announced Saturday.

The changes go into effect at 4 a.m. Tuesday and apply to all travelers, regardless of vaccination status, coming from countries that are not on the "red list," according to Health Secretary Sajid Javid.

Previously, travelers to the UK did not have to take a COVID-19 test if they were fully vaccinated and had not been in a red list country.

UK officials also announced that Nigeria will be added to the red list, effective 4 a.m. Monday.

The changes are to "slow the incursion of the Omicron variant," Javid said on Twitter.

Over 97% of Centers for Disease Control and Prevention employees are vaccinated, according to data released Friday by the Department of Health and Human Services.

Additionally, 99% of the agency's employees are "in compliance," meaning they have either initiated vaccination or have submitted a request for a medical or religious exemption.

In other HHS divisions, 96% of Food and Drug Administration employees are vaccinated and 99% are in compliance. At the National Institutes of Health, 97% are vaccinated and 99% are in compliance.

The data release comes as some Republican senators have pushed CDC Director Rochelle Walensky for vaccination rates at her own agency as she defends Biden's federal workers vaccine mandate, which is being challenged in federal court.

-ABC News' Cheyenne Haslett

The FDA has expanded its emergency authorization for Eli Lilly's monoclonal treatment for the treatment of mild to moderate COVID-19 to children under 12, including newborns, who have tested positive and are at risk for getting severely ill. This expansion also includes preventative use in young kids who may have been exposed and who are at high risk of getting severely ill.

This is the first time a monoclonal treatment has been authorized for children under 12.

-ABC News' Sasha Pezenik

Three cases of the omicron variant have been detected in Maryland, all among Baltimore area residents, Gov. Larry Hogan said.

One of these people, who is vaccinated, recently traveled to South Africa. The second case is someone in their household who is not vaccinated, Hogan said.

The third case is unrelated; this person, who is vaccinated, has no recent travel, Hogan said.

No one required hospitalization, he said.

At least 10 people have tested positive for COVID-19 on a Cruise Norwegian ship disembarking in New Orleans this weekend, according to the Louisiana Department of Health.

Those infected include both passengers and crew members, officials said.

The Norwegian Breakaway departed from New Orleans on Nov. 28 and stopped in Belize, Honduras and Mexico on its voyage. There are more than 3,200 individuals on board, the health department said.

The company required on-site testing in addition to proof of vaccination before boarding the vessel, according to the Port of New Orleans.

The health department said the cruise line has been adhering to appropriate quarantine and isolation protocols. In addition, everyone aboard the ship will be tested for COVID prior to disembarking.

Those who test positive for COVID-19 on the ship will either travel by personal vehicle directly to their private residence or self-isolate according to current Centers fo Disease Control and Prevention guidelines in accommodations provided by Norwegian Cruise Lines.

"The health and safety of our guests, crew and the communities we visit is our highest priority, and we will continue to take all appropriate actions to ensure their wellbeing and protect public health," a Norwegian Cruise Lines spokesperson told ABC News.

"We have identified a handful of COVID-19 cases among guests and crew onboard Norwegian Breakaway, which is scheduled to disembark in New Orleans, LA on December 5. All of the identified cases onboard are asymptomatic. In addition to requiring that 100% of guests and crew are fully vaccinated, per the Company's comprehensive health and safety protocols, we have implemented quarantine, isolation and contact tracing procedures for identified cases."

The spokesperson said the company is testing all individuals prior to disembarkation, and providing post-exposure and quarantine public health guidance by the CDC.

"Any guests who have tested positive for COVID-19 will travel by personal vehicle to their personal residence or self-isolate in accommodations provided by the Company according to CDC guidelines," the spokesperson said. "We take this matter extremely seriously and will continue to work closely with the CDC, the office of Governor John Bel Edwards, the Louisiana Department of Health as well as the city and port of New Orleans. At this time, there have been no changes to scheduled future sailings on Norwegian Breakaway. We will provide additional updates to impacted guests as appropriate."