The one-sentence letter didn’t say much. The coronavirus vaccine was “manufactured free of porcine materials,” Sinovac, the Chinese vaccine maker, wrote to Indonesia’s state-owned vaccine manufacturer in July.

While the letter was promising, Indonesian clerics needed more details. A vaccine laced with the smallest amount of pork DNA could dissuade some followers of Islam from inoculation in Indonesia, the country with the world’s largest Muslim population. Sinovac took months to provide more information, which came only this week.

The Chinese company’s delayed response has been yet another challenge in Indonesia’s already fragile vaccine rollout. With the highest number of coronavirus infections in Southeast Asia, the country is eager to drum up support for its goal of inoculating 181.5 million adults within 15 months. But looming questions about the safety of the Sinovac vaccine and whether it is halal, or allowed under Islam, are complicating the government’s efforts.

“There shouldn’t be any concern about whether this vaccine is halal or not halal,” President Joko Widodo said. “We are in an emergency situation because of the COVID pandemic.”

Indonesia has recorded nearly 800,000 infections and more than 23,000 deaths, staggering numbers in a region where virus cases have remained relatively low. Inoculations are set to begin with health workers, soldiers and police officers in the coming weeks, once health authorities are satisfied that the Sinovac vaccine is safe and effective.

Joko said he would go first to show there was nothing to fear.

The vaccine must also undergo a separate approval process by the Ulema Council, an influential group of Muslim clerics that decides which products are halal in Indonesia.

Islamic authorities in other countries where Muslims make up a sizable share of the population, including Malaysia and the United Arab Emirates, have already ruled that coronavirus vaccines are permissible, even if they contain pork gelatin, which is used to stabilize many inoculations.

Last month, the Vatican released a statement declaring coronavirus vaccines “morally acceptable” for Catholics who might be opposed to a vaccine developed with stem cells from fetuses aborted decades ago.

Indonesians are still waiting for religious leaders to weigh in.

“In pharmaceutical products, halal is one of the important elements after the safety, efficacy and quality of the vaccine itself,” said Bambang Heriyanto, a spokesman for Bio Farma, Indonesia’s state-owned vaccine manufacturer.

The Ulema Council is expected to issue a decree, or fatwa, authorizing the use of the Sinovac vaccine in the coming weeks, but the nature of its findings could affect how widely it is accepted in Indonesia, especially among the country’s many conservative Muslims.

During a measles outbreak in 2018, the government, backed by the World Health Organization, undertook an ambitious vaccination program, but the only vaccine available in sufficient quantities contained pig products.

After analyzing the measles vaccine, the Ulema Council declared it haram, or forbidden under Islam, but said its use was allowed because the outbreak was an emergency.

In some parts of the country, however, local Muslim leaders opposed using a haram vaccine. The program fell well short of its 95% target and ended with nearly 10 million children unvaccinated. Only 72% of the target group was vaccinated.

On billboards above the busy streets of Jakarta, the capital, a woman wearing a face mask and head scarf can be seen flexing her arm as images of the coronavirus float nearby. Thousands of such billboards and banners have been erected along high-traffic roadways across the country. The message: Vaccines protect you.

To encourage widespread vaccinations, some regional governments have also passed new laws allowing for the punishment of people who refuse to get inoculated against the coronavirus.

“The government will ensure that the vaccine is safe and effective, has minimal side effects and is, of course, halal,” said Wiku Adisasmito, spokesman for the national COVID-19 task force. “Regional governments will have the authority to make people obey and participate in the vaccination program so that herd immunity can be achieved easily.”

With a population of 270 million, Indonesia hopes to achieve herd immunity by vaccinating roughly two-thirds of the population in just over a year. Joko said Tuesday that he hoped it could be done even more quickly.

Indonesia has ordered vaccines from several companies but plans to rely mostly on Sinovac, which has already delivered 3 million doses. It is the only vaccine to have arrived in the country so far.

Bio Farma plans to manufacture 122.5 million additional doses using raw materials provided by Sinovac.

Like other countries, Indonesia is eagerly awaiting data from Stage 3 trials so that its Food and Drug Control Agency can evaluate the safety of Sinovac’s inoculation. Months ago, China began administering the Sinovac vaccine and one made by a second company, Sinopharm, even though human trials were not completed.

Sinovac is expected to release the findings of its late-stage trials soon, with approval by the Chinese government to follow. But China has rarely been forthcoming about its vaccine data and has a history of producing faulty vaccines and tainted food products. In 2018, a scandal erupted over substandard doses of a vaccine for diphtheria, tetanus and whooping cough, and over fabricated data for a rabies vaccine.

In Indonesia, a nationwide survey conducted in September by the health ministry, the WHO and UNICEF found that health issues were of even greater concern than whether a coronavirus vaccine was halal.

Dicky Budiman, an Indonesian epidemiologist at Griffith University in Australia, called on China to release scientific data from the inoculations so that Indonesia could evaluate the vaccines’ safety and effectiveness.

“Transparency is one of the biggest challenges for China, especially with their vaccines,” he said. “This is a crucial time for China to show the world how they have improved the quality of their vaccines.”

The Ulema Council said it had asked Sinovac repeatedly for documentation on the materials in the vaccine in order to make its determination. It is prepared to announce its ruling after Indonesia determines that the vaccine is safe and effective.

At the Global Halal Center near Jakarta, the council operates laboratories in biotechnology, physics, chemistry and microbiology that it has recently used to test Sinovac’s vaccine for pig products.

Its labs can test 500,000 product samples a year, said Muti Arintawati, director of the council’s Food, Drug and Cosmetics Analysis Agency. The council, founded in 1975 by representatives of major Islamic groups, has the authority to certify whether products and medications meet Islamic standards in Indonesia. Companies pay from $180 to $780 for the certification.

Major Islamic groups such as Nahdlatul Ulama and Muhammadiyah, which together have some 140 million members, will join the effort to encourage the vaccine’s acceptance once it has been deemed safe and a fatwa has been issued.

“We will give an explanation from the Islamic law perspective so that people are willing to be vaccinated,” said Ahmad Ishomuddin, Nahdlatul Ulama’s supreme leader. “I think only a small number of people will reject it because protecting life is a major purpose of religion.”