While the CDC initially recommended COVID-19 booster shots for a limited swath of Americans, last week they updated their guidance to allow all adults 18 and up to receive a booster.Data have pointed to breakthroughs among the earliest vaccine recipients, as well as older individuals and those with pre-existing conditions.On this week's episode, Katelyn Jetelina, PhD, MPH, an epidemiologist at the University of Texas School of Public Health in Dallas, walks us through what to watch for when it comes to breakthroughs, as more Americans travel this holiday season than since the start of the pandemic.