Restrictions, introduced 20 months ago in the early stage of the pandemic by then US President Donald Trump, had barred non-US citizens who were in Ireland and the other countries over the past 14 days.

This latest development will mean that family and friends on both sides of the Atlantic will be able to reunite again.

It is also expected to bring a welcome boost to airlines, including Aer Lingus, that are highly dependent on transatlantic traffic.

Last week, Aer Lingus Chief Executive Lynne Embleton said every seat on its flights to the US today had been sold.

The airline’s chief operating officer has described today as an important one for the airline, the tourist economy and the wider Irish economy.

Speaking on RTÉ’s Morning Ireland, Peter O’Neill said there were two flights to New York, one to Chicago and one to Boston today.

He said the plan was to rebuild additional flights, including to other destinations such as Newark, Orlando and San Francisco, over the coming weeks.

Mr O’Neill said the airline expects strong demand in the run up to Christmas, but the intervening winter period is more challenging.

However, he added that it is hoped that the airline’s capacity will be back up at 80% of 2019 levels by March 2022 and up to 90% by the summer period.

Travel agents have also welcomed the development, with the Irish Travel Agents Association President Paul Hackett saying it was already being reflected in higher bookings on the routes.

Inbound tourism operators in Ireland also expect that it will lead to a recovery in transatlantic route capacity and confidence among tourists, which in turn should help promote visits into the country.

The relaxation of restrictions will also make it easier for those working for the more than 650 Irish businesses with operations in the US, as well as those working for the 800 US multinationals with a presence in Ireland to move back and forth.

“We’re delighted to see the full reopening of travel to the US today as we believe full access to air connectivity between Ireland and the US is critical to the Irish economy,” said Mark Redmond, chief executive of the American Chamber of Commerce Ireland.

“This announcement restores the important ability for key Irish and US executives of US multinationals based here to travel to and from the US. And of equal importance, given that Ireland is the ninth largest investor in the US, it is also critical for the Irish companies with operations in the US.”

Although travel from the United States to Europe has been possible since the summer, foreign US residents holding certain visas have had no guarantee of being able to re-enter the country.

Lifting the travel ban will affect those travelling from more than 30 countries.

But entry to the US will not be totally unregulated: US authorities plan to closely monitor travellers’ vaccination status and will still require them to present negative Covid-19 tests.

From tomorrow, the US will require air passengers to be fully vaccinated and be tested within three days before travel. Airlines will be required to put in place a contact tracing system.

US health authorities have said all vaccines approved by the US Food and Drug Administration and the World Health Organization would be accepted for entry by air.

At the moment, this includes the AstraZeneca, Johnson & Johnson, Moderna, Pfizer/BioNTech, Covaxin, Sinopharm and Sinovac vaccines.