Ebola has taken its greatest toll on babies. About 90 per cent of children under age one, who caught the virus in West Africa, died from it, the first large study of the epidemic's impact on children said.

Those a little older - ages one to four - fared only a little better. Ebola proved fatal for nearly 80 per cent of them, the study found.

It is based on case sampling and tracking of more than 1,000 children by the World Health Organization's Ebola Response Team. The work was published as a research letter Wednesday by the New England Journal of Medicine.

Ebola has sickened more than 23,000 and killed more than 10,000 since the epidemic began more than a year ago. Guinea, Sierra Leone and Liberia have been hardest hit.

People over 16 make up 79 per cent of the confirmed and probable cases in which ages are known. The new report looks at the rest.

Key findings:

- Kids got sick faster: The average incubation period was about seven days in babies under one, and nearly 10 days in 10-to-15-year-olds. It can be as long as 21 days in adults.

- Nearly every child under age 1 had a fever, and all children under 16 were more likely to have this symptom than adults.

- Children were less likely than adults to report belly, chest, joint or muscle pain, or trouble breathing or swallowing, but that may be because young kids have trouble describing these things and not because their symptoms actually were different from those in older people.

- The death rate was lowest among children 10 to 15 years old. People over 45 fared almost as poorly as children under 5 in terms of survival.

The findings dovetail with what Doctors Without Borders has been seeing.

"Young kids don't do well," especially those under five, one of its physicians, Dr Armand Sprecher, said at an American Society of Tropical Medicine and Hygiene conference in New Orleans in November.

There are no specific drugs or vaccines to fight Ebola, but some experimental ones are being tested.

The study was supported by the Bill and Melinda Gates Foundation, the National Institutes of Health and others.