Measles cases could almost double in countries hardest hit by the West African Ebola outbreak as overwhelmed health systems are unable to maintain child immunizations, scientists said on Thursday.

For every extra month that health care systems are disrupted, international researchers said up to 20,000 children aged between 9 months and 5 years were put at risk.

"It could be a long time before the health care systems in the region recover from this," said Justin Lessler, an assistant professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, who co-led the study into the ripple effects of the Ebola epidemic.