fast --- Actually, the technologies used for these vaccine (specially mRNA ) production have been developing over many years. This pandemic was a good opportunity to use those technologies to produce the vaccines. (Here is a link to an article published in Nature about this) https://www.nature.com/articles/d41586-021-02483-w But I have to agree that the testing phases , authorization etc. were done much faster than usually done for a vaccine development due to the urgency of this situation.

Source author: Lakmini Premadasa lakminisurangika@gmail.com