The Washington Post has produced an exceptional work on vaccines and their progress. It does a wonderful job describing the complexity of vaccine development using infographics. Some of the key points.
Researchers in the United States set an audacious goal in January to develop a coronavirus vaccine within 12 to 18 months. This would be a world record. The mumps vaccine is considered to be the fastest to move, in four years, from scientific concept to approval in 1967. The quest for an HIV vaccine continues, 36 years and counting.
Coronavirus vaccines are moving much faster, partly because governments are taking on the financial risk of developing a vaccine that may not work. Through Operation Warp Speed, the U.S. government has invested about $9.5 billion to speed up development and jump-start manufacturing before research is finished. Recommended reading at
https://www.washingtonpost.com/graphics/2020/health/covid-vaccine-update-coronavirus/