Three health workers in Norway who recently received the AstraZeneca vaccine against Covid-19 are being treated in hospital for blood clots, Norwegian health authorities said.

Norway halted on Thursday the rollout of that vaccine, following a similar move by Denmark. Iceland later followed suit, Reuters reported.

“We do not know if the cases are linked to the vaccine,” Sigurd Hortemo, a senior doctor at the Norwegian Medicines Agency told a news conference held jointly with the Norwegian Institute of Public Health.

All three individuals were under the age of 50. The European medicine regulator EMA would investigate the three incidents, he added.