There are many governments rushing a vaccine. The only reason vaccine development has been slow is because it's usually done by the pharmaceutical companies. During the SARS outbreak they all spent millions developing a vaccine then SARS died back on its own. They're afraid the same thing will happen with this.
The main vaccine problem is testing and production. If a vaccine is developed in 90 days, then you need at least another 90 days of animal testing (probably longer), then human trials which could take another 90 days, then mass production starts which takes a long time to get going.
This whole process can be spread up if we get the pharmaceutical companies and governments involved in the mass production development, but that's unlikely to happen unless the deaths start hitting the tens of thousands.
All in all with a vaccine developed in 90 days, we're still looking at around 2 years until it can be distributed to everyone.