BERLIN—Germany’s government said Tuesday it will restrict the use of the AstraZeneca PLC’s Covid-19 vaccine for people younger than 60 following fresh blood-clotting incidents among recipients, potentially presenting the country’s sputtering vaccine rollout with fresh delays.

As of Wednesday, people under 60 will only be able to receive the vaccine if they specifically demand it, and if their request is granted by a physician, the government said Tuesday.

The decision comes 12 days after the European Medicines Agency or EMA, the EU drug regulator, said the vaccine was “safe and effective” and didn’t increase the risk of blood clots.

Chancellor Angela Merkel told reporters on Tuesday night that the change was prompted by the occurrence of what she called very rare but very serious cases of thrombosis among younger and predominantly female recipients of the vaccine.

“We cannot ignore those cases,” Ms. Merkel said. She added that the EMA and the World Health Organization were notified of the incidents.