Researchers working with pregnant women in Nigeria began to see an alarming surge in early infant deaths as COVID-19 spread. Their findings suggest the true toll of the pandemic has been much worse than official death statistics show.

The researchers were in Nigeria to study whether small payments to expectant mothers could improve child outcomes. They were still enrolling tens of thousands of women in four Nigerian states when COVID exploded into a global pandemic.

That chance of timing allowed them to monitor the pandemic’s effects on birth outcomes in almost real time. Infant mortality rates had been flat in the months leading up to the first cases of COVID in Nigeria. Then they arced upward. Within months, the researchers found, stillbirths increased by 22 percent, and newborn deaths increased by 23 percent.