The European Union (EU)'s drug regulator on Monday said it has concluded in its review that Moderna's COVID-19 vaccine's booster shot may be given to people aged 18 years and above, at least six months after the second dose.

It is the second COVID-19 booster vaccine to be approved in the EU.

"This follows data showing that a third dose of Spikevax given six to eight months after the second dose led to a rise in antibody levels in adults whose antibody levels were waning," the European Medicines Agency (EMA) said.

Earlier this month, the EMA approved Pfizer-BioNTech's booster shot and recommended a third dose of a shot from either Pfizer-BioNTech or Moderna for people with weakened immune systems. It left EU member states to decide if the wider population should receive a booster shot.

EMA on Monday said that the implementation of vaccination campaigns remains the prerogative of the advisory groups guiding the vaccination campaigns in each EU member state.

Under pressure to revive their economies, fight the more infectious Delta variant of the coronavirus and avoid further lockdowns in the winter, several EU member states launched their own booster campaigns before EMA guidelines. The different states have taken widely varying views on who is eligible.

The EMA said the risk of inflammatory heart conditions or other very rare side effects after a booster are being monitored.

U.S. authorities have authorized booster doses of Pfizer-BioNTech, Moderna and Johnson & Johnson.