for more traditional types...given the magnitude of COVID-19's threat and it's rapid transmission, time was of the essence in developing, testing and delivering of huge dosage numbers for the world's needs...thankfully, mRNA technology did that...and undoubtedly saved millions of lives...those 2 Danish physicians had nothing to say about what actually took place.
Check out the linked article on the Pros/Cons of mRNA vaccines vs. previous technologies.
Link: https://www.medicalnewstoday.com/articles/mrna-vaccine-vs-traditional-vaccine