After decades of work, the World Health Organization endorsed the first-ever malaria vaccine last year ¡ª a historic milestone that promised to drive back a disease that kills a child every minute.

In reality, efforts are falling well short of that, with a lack of funding and commercial potential thwarting GSK PLC's capacity to produce as many doses of its shot as needed, according to interviews with about a dozen WHO officials, GSK staff, scientists and nonprofit groups.

The British drugmaker committed to produce up to 15 million doses every year through 2028, following 2019 pilot programs ¡ª considerably less than the WHO says is needed. It is currently unlikely to make more than a few million annually before 2026, according to a source close to the vaccine rollout.