Indonesia, the world's fourth most populous country and once Asia's COVID-19 epicenter, has inoculated 29 percent of its population of 270 million people, using a variety of vaccine brands.

Budi told a House of Representatives hearing the government decided on boosters at the 50 percent mark due to vaccine inequity concerns at home or abroad.

"Issues of injustice or ethics are so high in the world, because some countries haven't gotten a lot of first shots," he said.

Given for free, Budi said the plan prioritises the elderly and the poor who are insured by the government, while the rest of the population may have to pay for them. Many health workers have already received boosters.

Australia begangiving boosters on Monday, while Britain and Germany have also agreed to give them. Thailand has given booster shots to recipients of the Sinovac vaccine over concerns about resistance to the Delta variant.