The regulator, which approved the jab for Europe, is due to offer a further update on Thursday after several European countries halted its use due to reports of some people suffering blood clots following vaccination.
Emer Cooke, the EMA’s executive director, told a press briefing on Tuesday there was no current indication that the Oxford/AstraZeneca’s coronavirus vaccine was the cause of the “very rare” reported blood clots.
“I want to stress at present there is no indication that vaccination has caused these conditions,” she said.
“They have not come up in the clinical trials and they are not listed as known side events with this vaccine.
“In clinical trials both vaccinated people and people who received the placebo have shown some very small number of blood clot developments.
“The number of thromboembolic events overall in vaccinated people seems not to be higher than that seen in the general population.”
Some countries have suspended use of a particular batch of the jab due to concerns, but Ms Cooke said the small number of reports from Europe involved several batches and “therefore it is unlikely to be something related to a specific batch”.
However, she said this would form part of the EMA’s ongoing investigation.
Some 30 cases of blood clots had been reported to the EMA by March 10 among almost five million people vaccinated, but additional cases had been reported over the weekend, Ms Cooke said.
She said there would be an increase in the reporting of such cases due to the publicity surrounding the current reports.
The EMA is looking at the incidence of blood clots and some reports of abnormally low levels of blood platelets among some people who have had the jab.
Ms Cooke said: “We have pulled together an ad hoc meeting again today to help us evaluate these cases with all the surrounding information that the member states will have.
“The experts will then carry on their assessment and again will meet on Thursday to come to a conclusion on the full information that has been gathered, and to advise us as to whether there are any further actions that need to be taken.
“We will inform the public of the outcome immediately after this meeting.
“Our experts are working tirelessly to carry out this assessment as quickly as possible, but it needs a scientific evaluation. We need to have the facts first. We cannot come to a conclusion until we have done a thorough scientific analysis and we owe it to the European citizens to deliver this clear and science-based response.”
She said that “trust in the safety and effectiveness of the vaccines we’ve authorised is paramount for us”, adding the EMA was worried “there may be an effect on the trust of the vaccines”.
But she said the priority was to ensure that vaccines “can be used safely”.
The World Health Organisation’s (WHO) global advisory committee on vaccine safety is also meeting on Tuesday to discuss the jab but has urged countries to continue using it.
Several European countries, including Germany, France, Italy Spain, Denmark and Norway have suspended rollout of the vaccine.
Sweden added itself to the list on Tuesday, saying the move was precautionary.
Ms Cooke was asked about reports of blood clots in relation to the Pfizer and Moderna vaccines, and how these compared with reports for AstraZeneca.
She said: “We are looking at adverse effects associated with all vaccines.
“At the moment the current focus, because of the reported instances in Europe, is of the AstraZeneca (vaccine) but we have looked at the background rates for all the vaccines currently in circulation and it looks like there are similar numbers coming in across the world.
“But that’s something that will have to be evaluated by our committee.”
Earlier, the director general of Italy’s medicines authority, Nicola Magrini, told Italian daily newspaper la Repubblica that the decision by some European countries to suspend the rollout was a “political one”.
He said the vaccine was safe and added: “We got to the point of a suspension because several European countries, including Germany and France, preferred to interrupt vaccinations… to put them on hold in order to carry out checks. The choice is a political one.”
According to AstraZeneca, about 17 million people in the EU and the UK have received a dose of the vaccine, with fewer than 40 cases of blood clots reported to date.
Peter Openshaw, professor of experimental medicine at Imperial College London, said the decision to pause rollout of the Oxford/AstraZeneca jab could be a “disaster” for Covid-19 vaccine uptake in Europe.
Asked what he would say to those in the UK who are booked to receive the vaccine, he told BBC Radio 4’s Today programme: “I really wouldn’t be worried at the present time.
“I think it is very clear that the benefits of being vaccinated at the moment so far outweigh the possible concern over this rather rare type of blood clot.
“It really is a completely one-sided argument statistically that we need to be vaccinating.
“I think it is a disaster for the vaccination uptake in Europe, which is already on slightly unsteady ground in some countries.”
Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), told Good Morning Britain that Covid was far more risky in terms of developing blood clots than any vaccine side effect.
He said: “It’s really important to remember that Covid is a vascular illness and causes clots all over the body.
“So, the risk of developing blood clots from Covid far, far exceeds any potential risk from the vaccination.”
Prof Harnden said he had “no doubt that this vaccine is safe and effective”, adding: “What I don’t understand is the nuances behind the Europeans’ decisions and their data, and that will become apparent in the next few days I hope and will be filtered through our regulator.”