Bill Gates has warned the world would be "vulnerable" to a quick-spreading deadly flu outbreak.
The billionaire philanthropist said the Ebola and Zika outbreaks exposed weaknesses in the ability to swiftly tackle health crises.
Mr Gates, whose foundation has pumped billions of pounds into vaccines and improving health systems in developing countries, said the development of new drugs can also be improved.
He told the BBC Radio 4 Today programme: "When we've seen Ebola or even now Zika, we realise we still haven't done enough.
"Our ability to create new drugs and vaccines quickly where we have an emerging disease, our emergency response system where we get people in and try and stop these epidemics - we don't have a strong enough system."
He said countries are grappling with how to ensure that regulatory, liability and organisational boundaries do not slow down the response to health crises.
He said: "So I cross my fingers all the time that some epidemic like a big flu doesn't come along in the next 10 years.
"I do think we'll have much better medical tools, much better response, but we are a bit vulnerable right now if something that spread very quickly, like a flu that was quite fatal.
"That would be a tragedy, and new approaches should allow us to reduce that risk a lot."