A vaccine against tuberculosis, the world’s deadliest infectious disease, has never been closer to reality, with the potential to save millions of lives. But its development slowed after its corporate owner focused on more profitable vaccines.

Ever since he was a medical student, Dr. Neil Martinson has confronted the horrors of tuberculosis, the world’s oldest and deadliest pandemic. For more than 30 years, patients have streamed into the South African clinics where he has worked — migrant workers, malnourished children and pregnant women with HIV — coughing up blood. Some were so emaciated, he could see their ribs. They’d breathed in the contagious bacteria from a cough on a crowded bus or in the homes of loved ones who didn’t know they had TB. Once infected, their best option was to spend months swallowing pills that often carried terrible side effects. Many died.

So, when Martinson joined a call in April 2018, he was anxious for the verdict about a tuberculosis vaccine he’d helped test on hundreds of people.

The results blew him away: The shot prevented over half of those infected from getting sick; it was the biggest TB vaccine breakthrough in a century. He hung up, excited, and waited for the next step, a trial that would determine whether the shot was safe and effective enough to sell.

Weeks passed. Then months.