By 'vaccines against cancer', what they mean is 'the ability to create a vaccine against one particular cancer in one particular person", which would activate that person's killer T-cells to go after that particular cancer. Pity it's not as universal as the phrase implies.

Anyway, mRNA vaccines were being used for this and some potential vaccine replacements - until we had a need for a fast-as-possible vaccine against Covid19.

Those potential vaccine replacements in the works? Safety and efficacy studies are expensive - particularly if there's an already known-safe and known-efficacious vaccine available. End result: they were stalled

So, we had, essentially, gene-printing equipment, we already knew how to encapsulate that in lipid nanoparticles.

What we didn't have was the ability to make tens of millions of doses - or those safety and efficacy studies. Enter project warp speed...