Pork-derived gelatin has been widely used as a stabilizer to ensure vaccines remain safe and effective during storage and transport. Some companies have worked for years to develop pork-free vaccines: Swiss pharmaceutical company Novartis has produced a pork-free meningitis vaccine, while Saudi- and Malaysia-based AJ Pharma is currently working on one of their own.

But demand, existing supply chains, cost and the shorter shelf life of vaccines not containing porcine gelatin means the ingredient is likely to continue to be used in a majority of vaccines for years, said Dr. Salman Waqar, general secretary of the British Islamic Medical Association.

Spokespeople for Pfizer, Moderna and AstraZeneca have said that pork products are not part of their COVID-19 vaccines. But limited supply and preexisting deals worth millions of dollars with other companies means that some countries with large Muslim populations, such as Indonesia, will receive vaccines that have not yet been certified to be gelatin-free.