The U.S. will announce Thursday that all air travelers entering the country, including vaccinated passengers and returning Americans, must undergo COVID-19 testing no more than a day before their flight departure, The Washington Post reports. Fliers will be mandated to take a test the day before their flight takes off and may have to do so again three to five days after arrival as well. White House officials are reportedly also mulling requiring travelers to self-quarantine for seven days upon returning, with penalties imposed for failing to do so. The move is aimed at containing the spread of the new Omicron variant, first detected in South Africa but believed by experts to already have spread to much of the world. The United States currently requires unvaccinated air travelers to show proof of a test taken one day before their flights; the new policy would extend the same mandate to vaccinated travelers.