Since their debut just 18 months ago, three COVID-19 vaccines have saved an estimated 2.2 million American lives, changed the trajectory of a pandemic and inspired all manner of conspiracy theories.
Two of those shots prompt a recipient's own cells to manufacture a key piece of the coronavirus by following instructions encoded in messenger RNA, or mRNA for short. The vaccines developed by Pfizer and Moderna have revolutionized our approach to immunizations, and they've done so with blinding speed.
That's left many people yearning for something a bit more old-school.
