By Tom Avril STAFF WRITER
The first two COVID-19 vaccines to be distributed, one made by Pfizer Inc. and BioNTech SE, the other by Moderna Inc., are the first such drugs to consist of genetic instructions in the form of RNA: ribonucleic acid.
Cells in the arm use this blueprint to make harmless fragments of the coronavirus, prompting the immune system to make antibodies and other customized defenses should the person ever be exposed to the actual virus.
Both prevented more than 94% of infections in clinical trials. Some recipients experience a temporary fever, arm pain, or headache, but there is no evidence of any longterm complications.
Here is a step-by-step description of the process, written with guidance from University of Pennsylvania scientist Drew Weissman, whose work with former colleague Katalin Karikó, now at BioNTech, helped make the vaccines possible. tavril@inquirer.com