Germany is restricting the use of Astrazeneca's COVID-19 vaccine to those over the age of 60.
The decision follows reports of cases of blood clots known as cerebral sinus vein thrombosis.
Of some 2.7 million people who have received the shot, Germany's vaccine regulator has recorded 31 cases of the rare brain blood disorder, which resulted in 9 deaths.
All reports involved women aged between 20 and 63, with the exception of two cases.
The new limit is another setback in Germany's already sluggish vaccination campaign.
But Chancellor Angela Merkel said it was essential to maintain public trust.
"The recommendations of the Vaccine Committee are based on the knowledge that experts have gathered over the past few weeks on very rare but very serious cases of thrombosis in people who have been vaccinated with AstraZeneca. These are findings that the Vaccine Committee, and ultimately we too, cannot ignore."
Millions of doses of the AstraZeneca vaccine have been safely administered around the world.
Many European countries briefly stopped using the vaccine earlier this month while investigating rare cases of blood clots.
Both the European Medicines Agency and the World Health Organization said in response that the benefits of the jab outweighed the risks.
Nearly all countries have since resumed use of the vaccine, but France has restricted it to those over the age of 55.
This week, Canada also suspended plans to give the vaccine to younger people amid the same concerns about blood clots.