That's a very good question.
I would also put on the table the H1N1 pandemic, which ended much faster than expected. As colleagues have said, a lot of vaccine manufacturers actually felt burned because that pandemic ended earlier. They had put in massive investments and were unable to reap particular revenue streams.
I think we really need the public sector and the private sector to understand the risks associated with vaccine investments and to structure public procurement contracts and financial incentives to build capacity in a way the ensures that the world has a lot of vaccine capacity.
Remember, though, that having vaccine capacity and then being able to repurpose it to whatever new pandemic comes up are two very different matters. One needs to have the base, but one also needs to be able to repurpose it. That takes time. Still, having the base would be a lot better than not having it.