BRUSSELS (NewsNation Now) — The head of the European Medicines Agency says there is “no indication” that AstraZeneca vaccines are the cause of blood clots reported in some shot recipients. Those reports led several European countries to suspend the use of the vaccine.

The EMA’s Executive Director Emer Cooke said Tuesday that the agency is “firmly convinced” that the benefits of the AstraZeneca shot outweigh the risks, but an evaluation is ongoing.

Cooke said the agency was carrying out a case-by-case evaluation of incidents and was expected to complete a review on Thursday.

Sweden was the latest to join a swelling group of European Union nations choosing caution over speed Tuesday, even as international regulators said the data does not suggest the vaccine caused the clots and that vaccinations should continue.

The vaccine has been approved for use in adults in more than 50 countries and has been proven to be safe and effective in research done in Britain, Brazil and South Africa. But there have been concerns raised about how the vaccine data have been released, and some European leaders, including French President Emmanuel Macron, have questioned the vaccine’s effectiveness in older people, citing a lack of information.

“All the data we have seen about the AstraZeneca vaccine suggests it’s very safe and is saving people from dying of COVID,” said Dr. Paul Hunter, a professor of medicine at the University of East Anglia. “But this may be more of a perception problem because every time there is a vaccine issue, we hear the name ‘AstraZeneca’ soon after.”

In Britain, where 11 million doses of the AstraZeneca vaccine have been administered — more than any other country — there have been reports of about 11 people who developed blood clots after getting a shot. None were proven to have been caused by the vaccine.

Some doctors pointed out that since vaccination campaigns started by giving doses to the most vulnerable people, those now being immunized are more likely to already have health problems. Experts say that could make it difficult to determine whether a vaccine is responsible.

Blood clots that form in the arms, legs or elsewhere can sometimes break free and travel to the heart, brain or lungs, causing strokes, heart attacks or a deadly blockage of blood flow.

Britain first authorized the vaccine based on partial results that suggested the shots were about 70% effective. But those results were clouded by a manufacturing mistake that led some participants to get just a half dose in their first shot — an error the researchers didn’t immediately acknowledge. When it recommended the vaccine be licensed, the EMA estimated the vaccine’s efficacy to be about 60%.

Europe has the luxury to be able to pick from several vaccine candidates — but the decision is still not an easy one on the continent, where the virus is again picking up speed.

The choice may be even more fraught elsewhere because many countries are relying heavily on AstraZeneca, which is cheaper and easier to handle than some other shots. The vaccine has so far played a huge role in the global initiative to ensure vaccines get to poorer countries known as COVAX.

Thailand last week was the first country outside Europe to temporarily suspend using the AstraZeneca vaccine, only to recant on Tuesday — when its prime minister received a dose.

“There are people who have concerns,” Prayuth Chan-ocha said after getting the shot. “But we must believe doctors, believe in our medical professionals.”

In the U.S., the Food and Drug Administration suspended a study in 30,000 Americans for an unusual six weeks, as frustrated regulators sought information about some possible side effects reported in Britain.

While the two-dose vaccine has received emergency clearance from the European Union and World Health Organization it has not from the U.S.

But President Joe Biden’s administration is stockpiling tens of millions of doses of the shot. America’s partners are prodding Biden to release his supply, noting that the administration has lined up enough doses of three already-authorized vaccines to cover every American adult by the end of May and the entire U.S. population by the end of July.

AstraZeneca says that the U.S.-produced vaccines are “owned” by the U.S. government and that sending them overseas would require White House approval.

“We understand other governments may have reached out to the U.S. government about donation of AstraZeneca doses, and we’ve asked the U.S. government to give thoughtful consideration to these requests,” Gonzalo Viña, a spokesman for AstraZeneca, said in a statement.