New travel rules for the United States: what you need to know about the changes due to the omicron variant

(CNN) -- Just when we thought America's travel requirements were starting to stabilize, the omicron variant enters the picture.

The dominoes began to fall rapidly after South African health authorities informed the world of the discovery of the omicron variant of the coronavirus in late November.

The Biden administration has established controversial travel bans on arrivals from eight southern African countries. The travelers found themselves unexpectedly stranded. And now the US authorities have announced that they will toughen travel regulations again.

Things change every day and even every hour, but here are the new requirements that apply from this Monday, December 6.

Are the requirements for omicron tests to enter the United States change?

Yes, according to the announcement made this Thursday by President Joe Biden of the new measures aimed at curbing the pandemic. All travelers Internationals entering the country will have to undergo a test within 24 hours before leaving for the United States.

This new deadline will apply to everyone, "regardless of nationality or vaccination status," says the plan outlined on the White House website.

According to the published plan, the tightening of the testing protocol will occur "early next week."

Currently, vaccinated travelers must be tested within three days of departure. Foreign travelers arriving in the United States must be fully vaccinated.

Unvaccinated Americans and legal permanent residents may enter the country with a test performed within one day of leaving for the United States. The new norm will make the term of the test one day for everyone.

Biden also announced that the federal mandate requiring travelers to wear face masks at airports, on planes and on other public transportation such as trains and buses has been extended through March 18.

Is there a post-arrival testing or quarantine requirement?

No. "We are not going to announce any measures on post-arrival testing and quarantine," a senior administration official told a news briefing on Wednesday night.

"I will say... look, if additional measures are recommended, if additional measures can be implemented well and are effective, we will not hesitate to take them, but we are not taking them today," the official said, according to a transcript from the White House of that briefing.

Which countries are included in the new US travel ban?

The travel bans announced on November 26 bar non-citizens from eight southern countries from entering the United States from Africa. These are Botswana, Lesotho, Malawi, Mozambique, Namibia, South Africa, Swaziland and Zimbabwe.

On November 27, the CDC placed all of these countries at "very high" risk level 4 for covid-19. (Botswana was already at Tier 4 due to its case load, more than 500 per 100,000 residents in the last 28 days.)

Citizens of those nations and those of others who have traveled there in the past 14 days are barred from entering the United States.

Can US citizens already in those nations return?

Yes, they can.

According to the White House statement, the CDC says that "citizens and lawful permanent residents of the United States, certain family members, and others who meet the specified exceptions, who have been in one of the countries above in the last 14 days will be allowed to enter the United States."

Until December 2, they are still required to follow current rules for re-entry: a negative covid-19 test within three days prior to travel if fully vaccinated and within one day if they are not vaccinated.

Can US citizens continue to travel to prohibited countries?

Technically, yes.

At least two US airlines continue to fly back and forth from South Africa, for example. Delta Air Lines continues to offer Atlanta-Johannesburg service, and United Airlines continues to offer Newark-Johannesburg service.

United Airlines is also resuming nonstop service between Newark and Cape Town, according to a South African Tourism press release. The statement also says that "we would like to underline that our country remains open for all those travelers who wish to visit it."

Whether it is advisable to go is another matter. The CDC advises against it.

You may also encounter new barriers to travel. For example, Zimbabwe imposed a mandatory lockdown starting Tuesday, November 30, and a mandatory quarantine for travelers, the state news agency NewZiana reported.

Going to southern African nations while worldwide bans are in effect may get you banned from other countries. For example, the UK does not allow entry to anyone who has been to the "red list" countries, which includes Angola and Zambia, in addition to the eight mentioned above, except for its own returning citizens.

Argentina, Canada, Italy and other nations have also established bans, each with their own specific parameters.

What is the United States doing to detect the virus?

The CDC said it would expand omicron screening at four major international airports in the United States.

The CDC also confirmed to CNN on Wednesday that authorities have ordered airlines carrying passengers who have been to certain southern African nations to share those passengers' contact information with the agency.

Airlines have already been collecting contact information from passengers under a CDC contact tracing order that has been in effect since November 8.

-- CNN Travel will update this article as new information becomes available and regulations change. Wayne Chang, Kaitlan Collins, Jacqueline Howard, Pete Muntean, Megan Vazquez and Greg Wallace contributed reporting.