April 7 (Reuters) - Europe's drug regulator on Wednesday found a possible link between AstraZeneca's COVID-19 vaccine and rare blood clots in adults who had received the inoculation.

The announcement is a fresh setback for the vaccine, which is sold at cost, for a few dollars a dose, and is by far the cheapest and most high-volume launched so far.

The following are reactions to the latest developments.

EMER COOKE, EXECUTIVE DIRECTOR OF EUROPEAN MEDICINES AGENCY (EMA)

"The risk of mortality from COVID is much greater than the risk of mortality from these rare side effects."

DR. SABINE STRAUS, CHAIR OF EMA'S SAFETY COMMITTEE (PRAC)

"This is not unexpected. We know that we are rolling out vaccines on a very large scale ... we will see events occurring ... some of them by chance."

DR. JACQUES BATTISTONI, HEAD OF FRENCH DOCTORS' UNION MG

"This time, the EMA confirms clearly that there is a link between vaccination and serious adverse effects. But these events are exceptional.

"Other medications also pose such risks.

"Will vaccination with AstraZeneca be harder? Most certainly. We will need to explain further and convince our patients that the benefits outweigh the risks, and that 'zero risk' just does not exist.

"We have a lot work ahead of us. However, we cannot give up on the AstraZeneca, we do not have enough doses to allow that."

WEI SHEN LIM, CHAIR OF BRITAIN'S JOINT COMMITTEE ON VACCINATION AND IMMUNISATION (JCVI)

"We are not advising a stop to any vaccination for any individual in any age group. We are advising a preference for one vaccine over another vaccine for a particular age group, really out of the utmost caution, rather than because we have any serious safety concerns."

"Those who have received their first dose of AstraZeneca vaccine should continue to be offered the second dose of AstraZeneca vaccine, according to the set schedule."

PROFESSOR ANTHONY HARNDEN, DEPUTY CHAIR OF JCVI

"What is clear is that for the vast majority of people the benefits of the Oxford AZ (AstraZeneca) vaccine far outweigh any extremely small risk and the Oxford AZ vaccine will continue to save many from suffering the devastating effects that can result from a COVID infection."

DAVID WERRING, PROFESSOR OF CLINICAL NEUROLOGY, UCL INSTITUTE OF NEUROLOGY

"We still urgently need more research to first understand which individuals are at highest risk of these unusual blood clots in the brain, which although very rare, can often be serious or fatal."

DR. MICHAEL HEAD, SENIOR RESEARCH FELLOW IN GLOBAL HEALTH, UNIVERSITY OF SOUTHAMPTON

"The Oxford AstraZeneca vaccine is a vital tool in the global strategy to contain the pandemic. It is being manufactured in large numbers, is stored at refrigeration temperatures and thus easier to transport, cost per dose is cheap, and key to the COVAX distribution to low- and lower-middle income countries.

"Maintaining public confidence is so important. An open, transparent process to assessing safety concerns must be part of that."

DR. WILLIAM SCHAFFNER, AN INFECTIOUS DISEASE EXPERT AT VANDERBILT UNIVERSITY MEDICAL CENTER IN NASHVILLE

"This is a classically difficult risk-benefit analysis. We know that no vaccine is totally free of adverse events, even the occasional serious adverse event, and this is a serious event."

"We're in this very difficult circumstance because this vaccine should be the cheapest and can be handled easily in normal refrigerator temperatures. It was probably going to be the dominant vaccine internationally, and that makes all of this much more poignant."

DR. AMESH ADALJA, AN INFECTIOUS DISEASE EXPERT AT THE JOHNS HOPKINS CENTER FOR HEALTH SECURITY IN BALTIMORE

"Even if the blood clots could be causally linked to the AstraZeneca vaccine, the risk-benefit ratio still favors the vaccine."

"I think that every negative headline about the AstraZeneca vaccine is going to add to vaccine hesitancy because, in general, the public doesn't remember any of the details or how low the risk is. What they remember is the headline."

(Compiled by Reuters staff Editing by Kevin Liffey, Matthew Lewis and Alison Williams)