The unprecedented speed of the COVID-19 vaccines was due to multiple factors.
Candidates for an mRNA vaccine — the technology used for the Pfizer/BioNTech and Moderna vaccines — can be quickly designed once scientists know the genetic sequence of the virus and which protein to target. Researchers already knew from past experience with SARS and MERS, which are other diseases caused by coronaviruses, that the spike protein the virus uses to enter cells was likely the right one.
Similarly, Johnson & Johnson has been researching adenovirus-based vaccines — the technology its COVID-19 vaccine uses — for many years in working on vaccines for HIV and Zika, and its Europe-approved Ebola vaccine.
The testing of the vaccines was also sped up by consolidating some of the early testing stages. Companies typically don’t want to proceed with expensive trials until there’s a sign the vaccine will work, but the government took on that financial risk in many cases.
The phase 3 randomized controlled clinical trials were also fast because high levels of disease transmission meant COVID-19 cases quickly accumulated among trial participants. And production capacity was sped along by starting manufacturing even before knowing whether the vaccines would be successful.