Norway will delay a decision on whether to resume the use of AstraZeneca's Covid-19 vaccine until 15 April, the Norwegian Institute of Public Health has said. 

Authorities suspended the rollout of the vaccine on 11 March after five healthy younger inoculated people were hospitalised for a combination of blood clots, bleeding and a low count of platelets, three of whom later died. 

"We still need more information and more knowledge to reach a conclusion," Sara Viksmoen Watle, senior physician at the Norwegian Institute of Public Health, told Reuters. 

"Now we have more of an explanation for why the patients got these symptoms... But we still do not know if it is caused by the vaccine. And if it is caused by the vaccine, why?" 

Norway is one of over a dozen European countries to have suspended the rollout of the vaccine, although most, including Ireland, have since resumed its use on the advice of the European Medicines Agency (EMA). 

The shot remains on hold in Denmark, however, while other Nordic countries are just using it for older age groups. 

The EMA has said the shot's benefits outweigh the possible risks. The World Health Organization has also backed it. 

AstraZeneca has said a review of safety data from more than 17 million people inoculated in Britain and the European Union showed no evidence the vaccine raised the risk of blood clots.