Messenger RNA, or mRNA, vaccines are a newer kind of vaccine. They carry a tiny piece of genetic information to show a body’s cells what the COVID-19 virus looks like — and how to fight it — without actually being infected. This blueprint teaches cells to make “spike proteins” (like the ones you see on illustrations of COVID), which allows the immune system to produce antibodies and develop memory cells for fighting the real virus if they become infected. Pfizer and Moderna’s COVID vaccines are mRNA vaccines.
https://www.yalemedicine.org/news/covid-19-vaccine-comparison (Yale Medicine)
https://publichealth.jhu.edu/2021/the-long-history-of-mrna-vaccines (Johns Hopkins Medicine)