I read this from the NY Times on how it works.
Pfizer and BioNTech are testing a vaccine that uses a genetic molecule called RNA to cause our own cells to make a viral protein. Our immune systems encounter the protein and make antibodies and immune cells that can recognize the protein quickly and deliver a swift attack. Moderna is in late-stage trials with an RNA vaccine of its own, and early clinical trials on other RNA vaccines are underway in China, England, India, Singapore, South Korea, and Thailand.
But the news from Pfizer and BioNTech could be heartening to other vaccine developers as well. Pfizer and BioNTech’s vaccine causes our bodies to make a viral protein called a spike. A number of other vaccines deliver the spike protein into the body, or just a fragment of it, that triggers the immune system to recognize it. Still other vaccines are based on other viruses, which harmlessly deliver a gene for the spike protein into cells. If the spike protein prompts a strong protection to the coronavirus, then all of these vaccines might also deliver encouraging results in the months to come.