The European Union drug regulator has issued long-awaited guidance on boosters for coronavirus vaccines. It says member states "may consider" giving a third Pfizer-BioNTech shot to people aged 18 and older.
The European Medicines Agency made the recommendation on Monday in a policy shift from its earlier stance.
The EMA previously maintained that priority should be given to fully vaccinating as many people as possible before beginning booster shots.
The agency on Monday stated that a third dose of the Pfizer or Moderna vaccine may be given to people with severely weakened immune systems, at least 28 days after their second dose.
The EMA also issued a recommendation for people with normal immune systems based on data showing the efficacy of the Pfizer vaccine.
The agency said that booster shots may be considered at least six months after the second dose for people 18 and older.
The EMA said its committee is currently evaluating data to support a booster dose for the Moderna vaccine.
France and Germany started administering booster shots to the elderly and other vulnerable people last month.