DAKAR, Senegal (AP) — A crisis over the supply of medical oxygen for coronavirus patients has struck nations in Africa and Latin America, where warnings went unheeded at the start of the pandemic and doctors say the shortage has led to unnecessary deaths.

It takes about 12 weeks to install a hospital oxygen plant and even less time to convert industrial oxygen manufacturing systems into a medical-grade network. But in Brazil and Nigeria, as well as in less-populous nations, decisions to fully address inadequate supplies only started being made last month, after hospitals were overwhelmed and patients started to die.

The gap in medical oxygen availability “is one of the defining health equity issues, I think, of our age,” said Peter Piot, director of the London School of Hygiene & Tropical Medicine, who said he survived a severe coronavirus infection thanks to the oxygen he received.

Doctors in Nigeria anxiously monitor traffic as oxygen deliveries move through the gridlocked streets of Lagos. Desperate families of patients around the world sometimes turn to the black market. Governments take action only after hospitals are overwhelmed and the infected die by the dozens.