Could a Vaccine Warning Label Hurt Moderna and Pfizer?

After coronavirus vaccines began to roll out, Moderna (NASDAQ:MRNA) and Pfizer (NYSE:PFE) emerged as the safest options; their mRNA vaccines weren't associated with any major side effects. At the same time, AstraZeneca and Johnson & Johnson -- makers of more traditional vaccines -- saw use of their vaccines slip. That's after a small number of individuals who received the AstraZeneca or J&J jab developed rare but sometimes deadly blood clots.

In recent weeks, however, Moderna's and Pfizer's safety situation has changed. Some teens and young adults developed heart inflammation following vaccination with their products; most of the cases happened in males. Now, the U.S. Food and Drug Administration (FDA) plans to include a warning statement in the product fact sheets.