Europe's drug regulator has found a possible link between Johnson & Johnson's Covid-19 vaccine and rare blood clotting issues in adults who received doses in the United States, but backed its overall benefits against any risks.

The European Medicines Agency (EMA) said on Tuesday its safety committee had concluded that a warning about unusual blood clots with low platelets must be added to the vaccine's labels, just as has also been required of rival shot maker AstraZeneca.