A Dutch medicines watchdog says it has received 10 reports of possible side effects after vaccinations with the Oxford AstraZeneca jab.
The national body responsible for reporting adverse drug reactions made the disclosure after the Dutch government became the latest to pause use of the vaccine as a precaution.
The Pharmacovigilance Centre Lareb said side effects seen included possible cases of thrombosis or embolisms, but not of a lowered number of platelets, as has been reported in Denmark and Norway.
Ireland on Sunday temporarily suspended the rollout of the AstraZeneca coronavirus jab, after Norway reported that one person had died and three had been admitted to hospital after receiving the shot.
AstraZeneca has insisted the jab is safe, claiming data from the 17 million vaccine doses so far provided no evidence of an increased risk of pulmonary embolism, deep vein thrombosis or low levels of platelets.
The World Health Organisation said on Friday that there was no reason to stop taking the shots.
The UK has administered more than 25 million vaccine doses - many of the AstraZeneca shot - without raising any alarms over clotting and the UK's Medicines and Healthcare Products Regulatory Agency (MHRA) has stressed there is currently no evidence that the vaccine causes blood clots.
The scare is the latest headache for the UK-Swedish drug giant, and means a shot which was meant to be a cornerstone of the global effort to vaccinate the world out of the pandemic has instead been dogged by controversy on several fronts.
The latest health concerns come on top of an intense political row with EU governments about the speed of vaccine deliveries.
Politicians halting use of the shot were acting from an abundance of caution, but risk hurting global efforts to vaccinate, Helen Petousis-Harris, a vaccine safety expert at the University of Auckland, told Bloomberg.
“You have to be very careful because it’s also sending a message that there could be something very wrong with the vaccine when in fact, it’s very unlikely that there is,” she said.
“We’re doing massive mass vaccination campaigns and people get sick all the time. We can’t panic every time it happens. But we also need to take all precaution. And it’s a hard balance.”