THE HAGUE: Europe's medicines regulator said Tuesday that blood clots should be listed as a "very rare" side effect of Johnson & Johnson's coronavirus vaccine, but that the benefits of the shot still outweighed the risks.

The United States is expected to announce its decision on the single-shot J&J vaccine by Friday, as nations around the world urgently try to accelerate inoculation campaigns and revive their pandemic-ravaged economies.

The European Medicines Agency (EMA) assessment came as an EU official promised to have enough doses available to vaccinate 70 percent of European adults by the summer -- a boon for the continent's sluggish rollout.

Europe's Johnson & Johnson campaign was delayed after US health regulators said the shot should be paused over blood clot fears.

After reviewing isolated cases of clotting among people who received the vaccine, EMA's safety committee said it found a "possible link" to the jab.

The regulator said its safety committee "concluded that a warning about unusual blood clots with low blood platelets should be added to the product information" for the J&J shot.

"This is a very rare effect," EMA chief Emer Cooke told reporters. "But it also makes it very important for doctors and patients to be aware of the signs so that they can spot any concerns."

Italy's health authorities said that in light of the EMA ruling, the vaccine should be considered "definitively safe" but the country would prioritise its use for people aged over 60.