Belgium is disregarding advice from the European Union's drug regulator and is imposing a four-week ban on administering the AstraZeneca vaccine to people aged under 56.
The European Medicines Agency said that even though it found a "possible link" between the AstraZeneca coronavirus vaccine and a rare clotting disorder, it placed no new restrictions on using the vaccine in people 18 and over.
The EMA insisted that the benefits of the shot still largely outweigh the risks.
Nevertheless, Belgium imposed a ban on administering it to younger people.
"We will keep it this way for the next four weeks and reassess it then," Belgian Health Minister Frank Vandenbroucke said.
He said the decision would have little impact on the vaccination campaign since few from that age group are in line to get jabs this month.