Trials began in 2020 for Pfizer. How long do medical trials for vaccines normally take? From what I've researched it takes years to complete trials, an it's usually 3 to 4 phases compared to 2 for covid vaccines.
mRNA vaccines — a new era in vaccinology - Nature Reviews Drug Discovery
mRNA vaccines represent a promising alternative to conventional vaccine approaches, but their application has been hampered by instability and delivery issues. Here, Pardi and colleagues discuss recent advances in mRNA vaccine technology, assess mRNA vaccines currently in development for cancer...
www.nature.com
Jan 2018, have a read.
Development of prophylactic or therapeutic vaccines against infectious pathogens is the most efficient means to contain and prevent epidemics. However, conventional vaccine approaches have largely failed to produce effective vaccines against challenging viruses that cause chronic or repeated infections, such as HIV-1, herpes simplex virus and respiratory syncytial virus (RSV). Additionally, the slow pace of commercial vaccine development and approval is inadequate to respond to the rapid emergence of acute viral diseases, as illustrated by the 2014–2016 outbreaks of the Ebola and Zika viruses. Therefore, the development of more potent and versatile vaccine platforms is crucial.