The Johnson & Johnson vaccine was recently described as a "game changer" for Ireland by Taoiseach Micheál Martin. Ireland has ordered 2.2 million doses, with 600,000 due between now and later in June.
Being a single-dose vaccine it is viewed as particularly useful. But the latest news that the US has paused its roll-out, to investigate rare blood clots, is a setback.
The hope is it will be a temporary pause. But the company has also delayed the roll-out of the vaccine in Europe as a result.
The Johnson & Johnson vaccine is made using the same technology as the AstraZeneca vaccine. It's called non-replicating viral vector.