Around the world, from Bangladesh to Nepal to Rwanda, vulnerable hot spots have been grappling with stalled COVID-19 vaccination programs as they run out of doses. Many of those shortages can be traced back to a single company: The Serum Institute of India.

The world’s largest vaccine-maker, Serum was last year named a top supplier of COVID-19 shots to COVAX, the World Health Organization-backed initiative aimed at securing an equitable global rollout. But the Indian company has been dogged by setbacks, from a ban on exports to a factory fire, that have hampered its ability to fill orders.

COVAX has pledged to send shots to some 92 countries, but has so far received only 30 million of the minimum 200 million doses it ordered from Serum, which was to provide the bulk of its early supply. Serum’s travails have now become a key illustration of how the effort to inoculate against COVID-19 has failed the developing world, and a cautionary tale for becoming over-reliant on one manufacturer amid a global crisis.