Developing a drug is expensive and drug companies typically wait for phase 2 studies to be complete before investing in phase 3 trials. Because of the pandemic, the United States and other countries provided funding to vaccine developers to start planning and enrolling patients in phase 3 trials at the same time that phase 2 trials were being performed. This greatly accelerated the drug development timeline without compromising the typical trial standards. Typically it takes a long time to enroll patients into a clinical study but during a pandemic enrollment was much easier. In order to prove efficacy you need enough positive results in the control group and since the prevalence of COVID-19 was so high they were able to achieve statistical significance early on.