The country's unprecedented creation and rollout of the vaccine were once considered a nearly impossible feat, given that vaccine development is often a long and arduous process, requiring years of regulatory and manufacturing hurdles to be overcome before it can be made available to the general public.

However, leaning on years of prior research on vaccine technology and with support from the federal government, the process was expedited, allowing for emergency authorization of the shots less than a year after work began.

"When the vaccine first became available a year ago, it seemed miraculous that a vaccine could be developed, rigorously tested in large clinical trials and ready to go in less than a year after the virus was identified," Dr. Stephen Morse, professor of epidemiology at Columbia University, told ABC News. "That's an amazing accomplishment considering that we really didn't have the infrastructure for a rapid national mass vaccination campaign when we started."