The EMA's Executive Director Emer Cooke said the agency's expert committee came to "a clear and scientific conclusion".
"This is a safe and effective vaccine whose benefits in protecting people from Covid-19 hugely outweigh the risks," she said but added that further studies would take place to probe possible links between the injection and rare blood clotting cases.
While millions of doses of the vaccine developed with Oxford University have been administered, small numbers of people have developed blood clots, which prompted countries including the European Union’s three largest nations – Germany, France and Italy – to suspend injections pending the EMA investigation.
The EMA's expert committee was convened at short notice to hold an emergency investigation into the cases of blood clotting.
Cooke said that the vaccine was not associated with an increased risk of thromboembolic events or blood clotting but did add that based on the available evidence "we still cannot rule out definitely a link between these cases and the vaccine."
In the report on its website the EMA said: "The vaccine may be associated with very rare cases of blood clots associated with thrombocytopenia, i.e. low levels of blood platelets (elements in the blood that help it to clot) with or without bleeding, including rare cases of clots in the vessels draining blood from the brain (CVST).
"A causal link with the vaccine is not proven, but is possible and deserves further analysis."
Cooke said the EMA was in favour of "raising awareness of the possible risks of the vaccine and making sure they are included in the product information."
"If it was me I would want to be vaccinated tomorrow but if something happened to me after vaccination I would want to know what to do about it and that's what we're saying today," said Cooke.
Chair of the EMA's vaccine safety committee Dr Sabine Strauss said there was no higher risk of thromboembolic events happening after being vaccinated in fact the risks may be reduced.
The EMA will carry out further studies into the vaccine. Those EU countries who paused the rollout of the AstraZeneca vaccine will not have decide whether to continue the injections after the EMA's conclusions.
'We have found the cause'
Earlier on Thursday, a group of health experts at Oslo University Hospital concluded that the blood clots in three health workers who took the AstraZeneca vaccine were triggered by an immune system response.
Three health care workers under the age of 50 were admitted to hospital with severe blood clots after taking the vaccine. One of the three later died of a brain haemorrhage.
“We have found the cause. There is nothing but the vaccine that can explain the immune reaction that occurred,” Pål Andre Holme, professor and chief physician at Oslo University Hospital told newspaper VG.
Holme led a team that worked round the clock to find out why the health workers were admitted to hospital with blood clots after taking the vaccine.
Asked about whether the EMA had taken into account the conclusions of Oslo University the agency's Dr Sabine Straus said committee had taken into account the cases in Norway but had not looked at the report from Norwegian health officials in Oslo.
The World Health Organization on Thursday renewed a call for countries to continue the use of AstraZeneca's
Covid-19 vaccine, shortly before expected assessments by EU and UN agencies.
The WHO's Global Advisory Committee on Vaccine Safety (GACVS) -- created in 1999 to address safety issues related to vaccines of potential global importance -- is due to publish the conclusions of its assessment of the safety of AstraZeneca's vaccine on Friday.
But as of now, "the benefits of the AstraZeneca vaccine far outweigh its risks and its use should continue, to save lives," the WHO's regional director for Europe Hans Kluge told a press conference.
"In vaccination campaigns, it is routine to signal potential adverse events. This does not necessarily mean that the events are linked to the vaccination," Kluge said
AstraZeneca billed as vaccine of choice
In Britain, which has administered more than 11 million AstraZeneca doses, experts see no evidence of more frequent blood clots among the inoculated.
Prime Minister Boris Johnson wrote in The Times newspaper that the shot “is safe and works extremely well”.
More than 382 million doses of Covid vaccines have been administered globally, the vast majority in wealthier countries while many poorer nations have yet to receive a single dose.
AstraZeneca’s shot, among the cheapest available, was billed as the vaccine of choice for poorer nations and the clot reports have had an impact beyond Europe.
Other countries that halted or delayed the rollout include Indonesia, Venezuela, Denmark, Norway, the Netherlands, Cyprus, Lithuania, Luxembourg and Sweden.
The pandemic spurred unprecedented efforts to develop vaccines, with a number of successful options now available.
Rollouts have been hampered by export controls, bitter diplomatic disputes and production issues – in addition to the AstraZeneca suspension.