How can a safe vaccine be made so quickly?

Vaccine development typically takes many years. However, scientists had already begun research for coronavirus vaccines during previous outbreaks caused by related coronaviruses (Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome). That earlier research provided a head start for rapid development of vaccines to protect against infection with COVID-19. No steps were skipped in the development of this vaccine but modifications to the process were made to shorten the timeline without sacrificing safety, such as: 

  • Overlapping phase I and phase II clinical trials. Phase I studies include a small number of people and evaluate whether the vaccine causes an immune response and is safe. Scientists looked at data from a group of people in phase I as phase II was progressing to make these evaluations. 
  • While completing large phase III trials, manufacturers began producing the vaccine, so that if it were shown to be safe and effective, they would have large numbers of doses ready. 
  • While waiting for a vaccine to be ready, many other aspects of vaccine delivery were prepared (e.g., developing plans for how to distribute the first, limited quantities available, ensuring adequate supplies for distributing and administering vaccine.)

More information is available at the CHOP website.