More than 23,000 people, mostly children, have been infected with measles in the Katanga region of the Democratic Republic of Congo. More than 400 have died, according to United Nations agencies and Doctors Without Borders.

In one village of 500, more than 30 children under age 5 died within two months — a third of all the children in that age group. “Their little graves are still visible in the cemetery,” said Augustin Ngoyi, the response coordinator for Doctors Without Borders.

The epidemic started in February, but as of early this month, the central government in Kinshasa had not acknowledged that it was underway and deaths were not being officially counted, he said.

Doctors Without Borders has vaccinated more than 300,000 children, but it has been difficult. The vaccine must be kept cold, and two shots, weeks apart, are needed for full protection.