British Transport Secretary Grant Schapps announced Tuesday that England will remove all southern African nations from its travel red list.

After the omicron variant was first discovered in South Africa and Botswana in November, several countries around the world, including England and the United States, imposed travel bans on a swath of nations in southern Africa.

The World Health Organization warned that blanket travel bans will not prevent the international spread of omicron, deemed a "variant of concern," and that restrictions place a heavy burden on lives and livelihoods.

The countries of Angola, Botswana, Eswatini, Lesotho, Malawi, Mozambique, Namibia, Nigeria, South Africa, Zambia and Zimbabwe will be taken off England's travel red list on Wednesday at 4 a.m. GMT, according to Schapps, who noted that all current testing measures remain in place.

"As always, we keep all our travel measures under review and we may impose new restrictions should there be a need to do so to protect public health," Schapps wrote on Twitter Tuesday.

Despite the travel bans, the heavily mutated variant has taken a foothold in London. British Health Secretary Sajid Javid told Parliament on Monday that omicron accounts for more than 44% of COVID-19 infections in the U.K. capital and it's expected to become the dominant variant there by Wednesday, overtaking the highly contagious delta variant.

Addressing Parliament again on Tuesday, the health secretary called omicron "a grave threat" and said the "race" to get as many people vaccinated and boosted "is new national mission."

"Scientists have never seen a COVID-19 variant that’s capable of spreading so rapidly," Javid said.

-ABC News' Christine Theodorou

The proportion of new cases of the omicron variant in the United States is steadily growing, according to new data released Tuesday by the Centers for Disease Control and Prevention.

The data show that omicron now accounts for 3% of all new COVID-19 cases nationwide, just over two weeks after it was first detected in the U.S. Last week, omicron was estimated to account for just 0.4% of all new cases nationwide. Epidemiologists, including Dr. John Brownstein, an ABC News contributor, cautioned that these figures are rough estimates.

Currently, the delta variant still accounts for the vast majority -- nearly 97% -- of new cases in the U.S., according to the CDC. More than half the country -- at least 34 states and Washington, D.C. -- have reported cases of the newly discovered variant.

-ABC News' Arielle Mitropoulos

A federal judge in New York has again declined to impose a preliminary injunction on the city’s COVID-19 vaccine mandate for public school employees.

The public school employees have said they have religious objections to the COVID-19 vaccine. The U.S. District Court for the Southern District of New York previously ordered a citywide panel to reconsider their requests for religious accommodation. Most of the plaintiffs were denied a second time and sought the injunction to prevent their termination.

In an order filed Tuesday, Judge Valerie Caproni found New York City's vaccine mandate to be rational, saying: "The Court has no facts before it on which it could conclude that the Citywide Panel’s process was irrational in any way or infected with hostility to religion."

The decision comes a week after the U.S. Supreme Court declined to take up a petition from health care workers who opposed New York state's vaccine mandate on religious grounds. As long as mandates are generally applied and do not single out a particular religion, the courts -- at all levels -- have allowed them to stand.

-ABC News' Aaron Katersky

An 83% surge in newly confirmed cases of COVID-19 during the past week in Africa, driven by the delta and omicron variants, is causing fewer deaths than previous surges, the World Health Organization said Tuesday.

But the WHO cautioned that more waves of COVID-19 infections could be building as updated forecasts warn Africa, the world's second-largest and second-most-populous continent, may not reach 70% vaccine coverage until late 2024.

Africa recorded more than 196,000 new cases for the week ending on Dec. 12, an increase of around 107,000 from the previous week, bringing the cumulative count since the pandemic began to 8.9 million cases, according to the WHO. The number of new cases is currently doubling every five days, the shortest reported this year. While the speed of the spread is fast, the WHO said, deaths remain low and even dropped by 19% last week compared with the previous week.

Africa is currently in its fourth wave of the pandemic, during which there were a little over 3,000 deaths reported in the first three weeks. About half as many cases were reported in the same time frame during the continent's third wave, which was fueled by the highly contagious delta variant, according to the WHO.

The WHO said this spike in infections coupled with low hospitalizations is particularly evident in South Africa, which saw a 66% rise in new cases last week compared with the previous seven days. While hospital admissions have jumped by 65% in the past week, the bed occupancy rate for intensive care units remains low at 7.5%, with 14% of the hospitalized patients receiving supplemental oxygen. Though the number of deaths also remain low, the WHO warned that this pattern may change in the coming weeks.

"We are cautiously optimistic that deaths and severe illness will remain low in the current wave, but slow vaccine rollout in Africa means both will be much higher than they should be," Dr. Matshidiso Moeti, the WHO's regional director for Africa, said in a statement Tuesday. "We've known for quite some time now that new variants like Beta, Delta or Omicron could regularly emerge to spark new outbreaks globally, but vaccine-deprived regions like Africa will be especially vulnerable."

As of Tuesday, only 20 African countries had vaccinated at least 10% of their population -- the global target the WHO had set for September 2021. Only six African nations have hit the year-end target of fully vaccinating 40% of their population, while just two countries -- Mauritius and Seychelles -- have reached the 70% coverage seen as essential for controlling the pandemic. At the current pace, the WHO estimates that it will take until May 2022 before Africa as a whole reaches 40% coverage and August 2024 before it reaches 70%.

"In a world where Africa had the doses and support to vaccinate 70% of its population by the end of 2021—a level many wealthy countries have achieved—we probably would be seeing tens of thousands of fewer deaths from COVID-19 next year," Moeti said. "But we can still save many lives if we can accelerate the pace of vaccination in early 2022."