Their breakthrough was creating mRNA molecules that contained psudeouridine instead of uridine. This modification allowed the mRNA to slip past the innate immune system and do its work.
I can't wait to see what mRNA vaccines and treatments we have in store in the coming decades. We already look like we will have a successful mRNA flu vaccine. With influenza in particular the speed of mRNA vaccine manufacturing is a real game changer as much of the effectiveness of flu vaccines rests on how well we can predict which strains will dominate the next season. Being able to make that prediction in the summer versus the winter before the next season would be a huge plus.