All US-bound passengers now need a negative COVID-19 test before boarding

All travelers flying into the U.S. must now provide proof of a negative COVID-19 test, taken no more than three days before their flight, or they will be denied boarding.

The order was initially announced by the Centers for Disease Control and Prevention on Jan. 12 and formalized in an executive order President Joe Biden signed last week.

International travel is still down considerably compared to last year, but there was an uptick in Americans flying to beach locales like Mexico that did not require them to quarantine upon arrival. This order is an attempt to mitigate the risk of travelers spreading COVID-19 as new variants of the virus emerge and the country struggles to roll out the vaccine.

"We urge folks to postpone their trips if they're able," acting Assistant Secretary of Consular Affairs Ian Brownlee said Tuesday, "and if they absolutely must travel to equip themselves with information."

Brownlee warned travelers will be responsible for covering their own lodging and medical costs if they test positive or cannot get a test while overseas.

"The bottom line message is this is really not a time for people to be engaging in discretionary travel, and that all travel should be postponed until we get a better handle on getting this virus under control and accelerate our vaccination strategies," CDC Director for the Division of Global Migration and Quarantine Marty Cetron said.

Here's what you need to know about the new travel rules:

Does the order apply to U.S. citizens?

The order applies to all travelers ages 2 and up, including U.S. citizens and legal permanent residents.

What kind of coronavirus test do I need to take?

Travelers can take a rapid, PCR, or an at-home test, as long as the specimen is laboratory tested. Travelers must bring written documentation of the laboratory test result -- paper or electronic.

If I have gotten the vaccine or tested positive for antibodies do I still need to take a test?

All travelers, regardless of vaccination or antibody status, have to provide a negative COVID-19 test or documentation of recovery.

What if I recently had COVID-19?

If you have proof of a positive COVID-19 test within three months and are safe to end isolation you can travel with documentation of the positive test and a letter from a health care provider or public health official that says you are cleared to travel.

What if my trip is shorter than 3 days?

You still need a test, but it can be done in the U.S. -- as long as its within the three-day window before your U.S.-bound flight.

Who checks the tests before boarding my flight to the U.S.?

Airlines are tasked with checking the negative test result or recovery documentation for all passengers before boarding. If the passenger does not have that, the airline is instructed to deny the passenger boarding.

What if I test positive when I'm abroad?

You must self-isolate and delay travel until you have recovered from COVID-19.

Are there any exemptions?

The CDC said exemptions "may be granted on an extremely limited basis when emergency travel (like an emergency medical evacuation) must occur to preserve someone’s life, health against a serious danger, or physical safety and testing cannot be completed before travel."

Do I have to quarantine when I arrive in the U.S.?

There is no mandatory quarantine, but the CDC recommends that travelers get tested three to five days after travel and stay home or self-quarantine for seven days.

"Even if you test negative, stay home for the full 7 days," the CDC said. "If you don’t get tested, it’s safest to stay home for 10 days."

ABC News' Conor Finnegan contributed to this report.