The EU has reversed its decision to temporarily override area of the Brexit deal amid an ongoing row over Covid vaccine supplies in the bloc.
The move could have seen checks at the border of Ireland and Northern Ireland to avoid shipments entering the UK.
However the European Commission later said it will make sure the Northern Ireland Protocol is "unaffected".
Boris Johnson had expressed "grave concerns" about the plan in a phone call with the commission's president.
President Ursula von der Leyen later tweeted to say she had held "constructive talks" with the prime minister.
She said they had "decided on the principle that there shouldn't be restrictions on the export of vaccines by companies where they are fulfilling contractual responsibilities".
The EC proposals had also sparked concern from Northern Ireland First Minister Arlene Foster and Irish prime minister Micheál Martin.
Mr Martin welcomed the EU's reversal, describing it as a "great development given the countless challenges we face in tackling Covid-19".
The Brexit deal guarantees an open border between your EU and Northern Ireland, without controls on exported products.
However, the EU got announced it could trigger a clause to introduce the export controls on vaccines to Northern Ireland.
On Friday, the bloc invoked Article 16 of the Northern Ireland Protocol in a bid to prevent the region learning to be a backdoor for EU vaccines to be sent to the wider UK. The EU previously said its actions had been "justified" to avert problems the effect of a lack of supply.
It had been not thought that the move would directly disadvantage Northern Ireland, which gets its vaccine supplies through the UK procurement system.
Despite backtracking on Northern Ireland, the EU continues to be introducing new controls giving member states the energy to block exports of the coronavirus vaccine to countries like the UK - as long as they want to.
It was the latest development in a good deepening dispute over the vaccine producer AstraZeneca's delivery commitments to the EU.
The bloc agreed to buy up to 400m doses of the AstraZeneca vaccine last year, and on Friday the EU's drugs regulator approved the vaccine's use for all adults.
But the firm explained that because of problems at among its EU factories, supplies will be reduced by about 60% in the first quarter of 2021.
In a statement released on Friday evening, a No 10 spokesman stated Mr Johnson had spoken to Mrs von der Leyen and expressed his "grave concerns" about the "potential impact" of the EU's actions on vaccine exports, urging it to "urgently clarify its intentions".