At least 15 children in South Sudan are dead after receiving a contaminated measles vaccine.
A joint statement from the World Health Organization and UNICEF says the children died of "severe sepsis/toxicity" after getting the vaccine.
And investigators say human error was to blame.
During a four-day immunization campaign in May, the vaccination team reportedly used the same syringe on every child and failed to properly store the vaccine.
Both the WHO and UNICEF expressed their "deep regret and sadness" for the incident.
The Associated Press reports health officials are continuing the measles vaccination campaign regardless. The campaign aims to help more than 2 million children in South Sudan.
According to data from the WHO, more than 1,600 measles cases have been reported across the country since the start of 2016. At least 19 of those cases were fatal.
Measles is just one of the many hardships South Sudan is facing. The country has been devastated by years of civil war, famine and a recent cholera outbreak.