IN OCTOBER, A NINE-MONTH-OLD BOY FROM KHYBER PAKHTUNKHWA was diagnosed with polio, the seventy-seventh case recorded in Pakistan in 2019. The boy’s parents did not vaccinate him, according to an article in the local newspaper, in part because they believed the polio vaccine was haram—prohibited under Islamic law.

It’s part of a recent cycle of vaccine refusal among parents across the Muslim world, leading to increases in disease. In 2018, vaccination rates fell to as low as 8% in some provinces in Indonesia after a fresh wave of confusion erupted over whether vaccines were acceptable under Islamic law. In one district, an outbreak of 800 cases of measles resulted in the deaths of 72 children.

Vaccine refusal is growing around the world, in affluent U.S. suburbs and remote villages in Afghanistan. In 2019 the World Health Organization identified “vaccine hesitancy”—refusing or expressing reluctance about vaccines—as one of the top 10 biggest threats to global health. A high percentage of the estimated 13.5 million infants worldwide who were not immunized in 2018 live in Muslim-majority countries.

For Muslims, it’s pork that is the main problem, as porcine gelatin is widely used in vaccine production, raising questions about whether the medicines are halal, or allowed under Islamic law. While consuming pork is forbidden, there are theological provisions that allow for vaccination, even when the vaccine contains pork byproducts. Because one purpose of Shariah law is to protect life, when disease risk is high, the benefits to life are seen to outweigh considerations of impurity.

Vaccines have also historically been subject to the Islamic principle of “transformation,” which says that if a forbidden product is fundamentally changed, in this case from pork to gelatin, it is permissible. These positions have been voiced repeatedly by groups of Islamic scholars and imams. In April 2019, for example, 30 Islamic religious scholars from Afghanistan and Pakistan gathered to issue a joint statement urging parents to vaccinate their children against polio. The statement declared that “polio vaccines are not only safe and in compliance with Islamic principles, but also a religious and moral duty incumbent on all parents.” Similar statements were made in 2014, in 2001and in 1995, when 112 leading Islamic scholars met under the Islamic Organization for Medical Sciences and ruled porcine in vaccines “clean.”

But there is no central governing body for the Muslim faith, so local imams can make their own individual pronouncements. In 2018, for instance, Indonesian’s top Muslim clerical body, the Ulema Council (MUI), issued a fatwah declaring that the pork products in the measles-rubella vaccine made it forbidden. The MUI quickly reversed its position, stating the vaccine was acceptable until a better alternative came along, but the damage had already been done. Fears about vaccines across the Muslim world had been circulating for some time, and were not helped by the U.S. search for Osama bin Laden, which used a fake vaccination program as a cover. Celebrities in the Muslim world—as in the West— have also voiced anti-vaccination sentiment on social media.

To address fears that vaccines are not halal, some drug companies began designing special halal vaccines that use bacteria or yeast in place of pork products as far back as a decade ago. Swiss pharmaceutical company Novartis, for example, has produced a pork-free meningitis vaccine since 2010, though some Muslims question its purity. Saudi and Malaysia-based AJ Pharma has a pork-free vaccine for polio and is in the process of developing a vaccine for meningitis that could be used by the millions of Muslim pilgrims who participate in the Hajj pilgrimage to Mecca each year. Saudi Arabia requires Hajj participants to provide proof of meningitis vaccination before entering the country.

In 2018, the Malaysian pharmaceutical company Pharmaniaga collaborated with Malaysia’s Ministry of Finance and India-based Hilleman Laboratories to produce halal vaccines for diphtheria and meningitis. That partnership is also planning to conduct clinical trials, manage regulatory matters and facilitate sales of a halal vaccine that it hopes to begin manufacturing in a new plant in Malaysia between 2020 and 2024. Indonesia’s state-owned pharmaceutical company Bio Farma, is also racing to design a halal form of the measles-rubella vaccine, in the wake of last year’s fatwah by the MUI.

Other companies are using experimental technologies to develop halal vaccines. Genetically engineered tobacco plants, for instance, can be used in place of animal products to manufacture vaccines, which may also have some advantages in terms of cost and efficiency, according to Michael Callahan, an infectious disease physician at Massachusetts General Hospital who led novel vaccine development for the research arm of the U.S. Department of Defense.

Getting new vaccines approved takes time, however. Executives at Bio Farma have said that it could take 15 to 20 years to ready its measles-rubella vaccine. Some worry that publicizing efforts to produce certified halal vaccines will encourage continued confusion in the meantime and spur more vaccine refusal among parents, resulting in preventable disease and death.

In the absence of halal vaccines, education and enforcement campaigns can help persuade parents to use existing products. Some countries have begun to levy heavy penalties for refusing vaccination, and in northwestern Pakistan, parents have been jailed for that offense. The Malaysian government has imposed jail terms of up to 10 years, citing child neglect.

In Muslim-majority Nigeria, a concerted multi-decade effort to wipe out polio shows what can happen when anti-vaccine sentiment is addressed. On August 21, the country marked three years since it reported a new case of polio, and Nigeria has been certified polio-free by WHO. “There were serious concerns and conspiracies about the vaccines in use, and that really set back the polio eradication efforts there,” says Walter Orenstein, director of the Emory Program on Vaccine Policy and Development at Emory University in Atlanta. “And that has been overcome by getting religious authorities to support vaccination, and by building trust.”