EXPLAINER: What are the rules for travelers entering the US?

President Joe Biden’s latest measures to limit the spread of COVID-19 will increase the hassle factor of flying into the United States, even for American citizens returning from overseas.

Beginning next week, travelers heading to the U.S. will be required to show evidence of a negative test for the virus within one day of boarding their flight. The previous period was three days.

Also, Biden will extend the federal rule requiring passengers on planes, trains and buses to wear face masks through March 18. It was scheduled to expire in mid-January.

Those proposals came about quickly, underscoring the urgency for the White House to act ahead of winter, when the virus can spread more easily among people indoors, and since the discovery of a worrisome new variant of COVID-19. The first U.S. case of the omicron variant was discovered in California and reported by the administration Wednesday.

The administration’s moves come just days after the White House announced a ban on travel to the U.S. by foreign nationals who have been to South Africa or seven other African countries within the previous 14 days. That travel ban does not apply to U.S. citizens and permanent residents.

More telling, perhaps, is what's not included in Biden's announcement, including some proposals that were floated earlier this week like new quarantine rules for people arriving in the U.S. from overseas, which travel industry officials said would have been highly disruptive.

White House press secretary Jen Psaki was asked why the administration didn't go further and require vaccination or a negative test for passengers on domestic flights. She replied that “nothing is off the table.”

“We base our decisions on the advice of the health and medical experts, what is going to be most effective and what we...