Is the Pfizer booster shot necessary? An expert weighs in

Pfizer's recent push to add a booster shot to its COVID-19 vaccination protocol seems to be at odds with what many people understood about the drug's effectiveness. And, as William Brangham reports, it has also prompted real concern among healthcare professionals. Dr. Kirsten Bibbins-Domingo, a professor of epidemiology and biostatistics at the University of California joins us to discuss.