To help prevent people from getting the Ebola virus, countries around the world paid to help doctors develop a new vaccine. Now that the vaccine has been made, doctors will need to experiment on a large number of people to find out if it works safely.

Testing a new vaccine on a large number of people raises questions about how to protect participants and ensure they give informed consent. These are ethical concerns, so the challenge is ethics. The fact that countries paid for the vaccine points to money, but the question asks about experimenting on people.

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