Washington Post: “The United States on Monday [December 6, 2021] began requiring all inbound international travelers to show proof of a negative coronavirus test taken within a day of their flight to enter the country. The requirement is mandatory for anyone at least 2 years old, even American citizens and legal residents, regardless of vaccination status. Previously, anyone flying into the United States needed to test ahead of their trip, but their vaccination status determined their testing timeline. Vaccinated travelers had three days to get tested, while unvaccinated travelers had just one. Other countries have also implemented new testing strategies to combat omicron. Starting Tuesday, the United Kingdom will require international travelers to show proof of a negative test within 48 hours of their inbound flights (in addition to testing again within two days of arrival and self-quarantining until results are processed). The updated testing requirements — along with the extension of federal mask mandates and expansion of voluntary testing opportunities for new arrivals at some U.S. airports — aim to slow the spread of the emerging omicron variant. Here’s what international travelers need to know ahead of their flights…”