COVID booster shots are now recommended for millions of Americans, prompting questions on why immunity acquired from the vaccines is waning so soon. Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, has hinted that periodic booster shots against COVID are likely here to stay, and may redefine what it means to be "fully vaccinated." While natural immunity from previous COVID infection is of scientific interest, it's also a political talking point that some have seized on to sidestep vaccination. What does the science show when it comes to the duration of natural immunity? And how does natural immunity compare to vaccine-acquired immunity? On this week's episode, Bob Wachter, MD, of the University of California San Francisco, answers questions about immunity and how to stay protected.