Germany, France and Italy have suspended the rollouts of the Oxford-AstraZeneca vaccine, after incidents in Europe involving blood clots.
The three countries have joined several smaller European nations who have stopped vaccinations as a precaution while checks are made.
The World Health Organization, WHO, has said there is no evidence that the incidents are caused by the vaccine.
It said it was reviewing reports relating to the jab, but it was important vaccinations continued.
It added that it was good practice to investigate potential adverse events.