The health ministry on Friday said that Malaysia has granted conditional approval for the COVID-19 vaccine made by Pfizer (PFE.N) and BioNTech (22UAy.DE) to be used as a booster shot.

The approval allows the vaccine to be used only on adults aged 18 and above, at least six months after they have received their second dose, the ministry said in a statement.

Authorities earlier said booster shots would not be compulsory but were highly recommended for those in vulnerable and high-risk groups.

The mixing of different vaccines will also be allowed for booster doses. In addition to the Pfizer-BioNTech shot, Malaysia uses vaccines made by Britain’s AstraZeneca (AZN.L) and Chinese firms Sinovac (SVA.O) and CanSino Biologics (6185.HK) in its national inoculation campaign.

About 64% of Malaysia’s 32 million population are fully vaccinated, including 89% of adults.

(This story has been refiled to correct paragraph 4 RIC of CanSino Biologics)