Indonesia President Joko Widodo said his country should not rush the introduction of vaccines, citing concerns over public awareness about whether they were halal.
Indonesia, the world's largest Muslim-majority nation, has reported more than 365,000 coronavirus cases and more than 12,000 deaths since the outbreak began.
The government has been racing to secure a supply of vaccines while they are still under development, drawing criticism from some epidemiologists for seeking a "silver bullet" solution before full vaccine efficacy and safety is known.
Senior ministers indicated that emergency vaccine authorisation could be granted as early as November.
But Mr Widodo, better known by his moniker Jokowi, signalled a more cautionary approach and gave a warning against being too hasty.
He called for clear public messaging about whether the vaccines were permissible under Islamic law.
"I ask that this vaccine is not rushed because it's so complex," Mr Widodo said.
"I want to ensure there is good preparation. On public communication, especially in relation to halal and haram, the price, and quality."
Coronavirus around the world
Indonesia previously pledged to vaccinate more than 100 million people next year, but Mr Widodo said on Monday that the scale of inoculation the country of 270 million people would be challenging.
Controversy over whether vaccines adhere to Islamic principles has stymied public health responses before in Indonesia, including in 2018 when the Indonesian Ulema Council issued a fatwa declaring a measles vaccine was haram.
Indonesia secured 50 million doses of a potential Covid-19 vaccine from China's Sinovac pharmaceutical company by March next year.
The country also secured 100 million doses from AstraZeneca by next April, in addition to other deals.
Vaccines from Sinovac, as well as Chinese companies Sinopharm and CanSino Biologics, for 9.1 million people will be available this year, with health workers prioritised, said Achmad Yurianto, a senior health ministry official.
Indonesia's rush to secure supplies of unproven vaccines generated concern among epidemiologists, some of whom argued the country should instead focus on testing and contact tracing until a safe and effective vaccine was available.
"Many countries think a vaccine will be their silver bullet to deal with the pandemic," said Dicky Budiman, an Indonesian epidemiologist from Australia's Griffith University.
"But unfortunately, the history of pandemics, the literature, does not support that."
