People who had contracted the coronavirus must provide proper documentation that they have recovered from it prior to boarding, the CDC added.
The negative test must be taken within 72 hours prior to arrival in Ireland.
All air passengers bound for the United States will require a negative Covid-19 test within three days of their departure, the Centers for Disease Control and Prevention (CDC) said Tuesday.
The CDC also recommends that travellers get tested again three to five days after their arrival, and stay home for at least seven days.
All air travelers aged two and older must follow the CDC order.
Passengers will need to show the documentation initially to an airline but must also retain it and produce it on request to any Us government official or "cooperating state or local public health authority".
The CDC order applies to USA citizens as well as foreign travelers. The agency said it delayed the effective date until January 26 to give airlines and travelers time to comply.
New Zealand announced new rules on Tuesday, which mean almost all Kiwis living overseas will soon have to show a negative Covid-19 test before boarding their flight home.
Canada imposed similar rules for almost all global arrivals starting January 7, as did many other countries. The new measures are created to try to prevent travellers from bringing in newer forms of the virus that scientists say can spread more easily.
"Testing does not eliminate all risk", said CDC Director Robert R. Redfield, MD.
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The health ministry also said it has identified the first case of a highly contagious United Kingdom variant in the country. The healthcare system for the country of 32 million people was at a breaking point, the premier said.
It is likely that the recently identified version of the virus from Britain is "in every state or most states", said Dr. Ashisha Jha.
Officials briefed on the matter said U.S. public health officials had essentially given up winning approval until president-elect Joe Biden took office.
"We will keep test standards and innovative testing technologies under review", he said.
COVID-19 is already widespread in the USA, with more than 22.8 million cases reported. And the country recorded 4,327 coronavirus-related deaths on Tuesday, a one-day record high.
The earlier requirement for United Kingdom travelers was a response to a new coronavirus variant that was recently identified in the UK.
Delta Air Lines acted quickly to waive any fare difference on worldwide flights to the US for tickets purchased on or before January 12, the day the CDC made the announcement, for travel through February 9.
Nicole Carriere is a spokeswoman for United Airlines.
Henry Harteveldt is a travel expert with Atmosphere Research Group.
The Associated Press reported this story. Ashley Thompson adapted it for VOA Learning English, with additional materials from Reuters news agency.
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