Nigeria, July 22 -- When 50-year-old Lawan Umar left home with his daughter, six-year-old Zulaihat, he believed she had a fever that would be treated at the hospital. He never imagined he would return to bury her.

Also, he could not have imagined that, within five days, he would also bury her siblings - Khadija, nine, and 12-year-old Umar. All three children died from diphtheria in October 2023, a year after Nigeria's ongoing diphtheria outbreak began in 2022.

"They waved at me when Zulaihat and I were leaving for the hospital," Mr Umar recalled with his eyes filled with tears. "They were smiling. They looked fine."

What started with a fever turned out to be the start of a heartbreaking chain of events. Zulaihat was first taken to a lo...