It has now been 6 months since the first wave of Americans received their first shot of a COVID-19 vaccine. Proving just how effective the vaccines are in the U.S., we've seen the virus spread down to levels not seen since the start of the pandemic. But one thing we still don't know: how long immunity will last. As Pfizer and Moderna move forward for full FDA licensure, executives at both companies have cited the need for a likely booster. Pfizer CEO Albert Bourla, DVM, PhD, predicted the need for a booster to be "somewhere between 6 and 12 months" after first being vaccinated. Explaining the key role variants will play in the decision, Moderna CEO Stéphane Bancel predicted it could be as soon as September for those at highest risk of severe infection. NIAID director Anthony Fauci, MD, told a Senate subcommittee that he would expect the need for a booster, but declined to put a timeline on his prediction. "I don't anticipate that the durability of the vaccine protection is going to be infinite," Fauci said. Researchers within his institute at the NIH recently began looking into, not just if boosters are necessary but also how to possibly mix vaccines and the impacts on protection. On this week's episode, William Schaffner, MD, professor of Preventive Medicine and Infectious Diseases at Vanderbilt University Medical Center in Nashville, joins us to help break down what the science tells us now, and what to expect.