Cause or coincidence?
The data supplied by AstraZeneca shows there have been 37 reports of blood clots among the 17m people across Europe who have been given the vaccine.
But the key question that has to be asked is whether this is cause or coincidence? Would these clots have happened anyway?
Adverse events like this are monitored carefully, so regulators can assess if they are happening more than they should.
The 37 reports of clots are below the level you would expect. What is more, there is no strong biological explanation why the vaccine would cause a blood clot.
It is why the World Health Organization and UK drugs regulators have all said there is no evidence of a link.
Even the European Medicines Agency, which is looking into the reports, has suggested the vaccine should continue to be used given the risk Covid presents to health.
Unsurprisingly, therefore, the decisions by individual nations to pause their rollouts have baffled experts.
Prof Adam Finn, a member of the WHO's working group on Covid vaccines, says stopping rollout in this way is "highly undesirable" and could undermine confidence in the vaccine, costing lives in the long-term.
"Making the right call in situations like this is not easy, but having a steady hand on the tiller is probably what is needed most."
From the BBC site.