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.

In Brazil’s Amazonas state, a pair of swindlers were caught reselling fire extinguishers painted to look like medical oxygen tanks. In Peru, people camped out in lines to get cylinders for sick relatives.

Only after the lack of oxygen was blamed for the deaths of four people at an Egyptian hospital in January and six people at one in Pakistan in December did governments address the problems.

John Nkengasong, director of the Africa Centers for Disease Control and Prevention, said medical oxygen is a “huge critical need” across the continent of 1.3 billion people and is a main reason that Covid-19 patients are more likely to die there during surges.