Between the rise of the delta coronavirus variant, fear of waning immunity due to breakthrough COVID-19 cases and the White House announcement that all adults will need a COVID-19 booster starting as early as Sept. 20, news has been flooded with unsatisfying advice and confusing timelines about if, and when, you’ll need a coronavirus booster. (If you’re a person with an immunocompromising condition who received an mRNA COVID-19 vaccine, you’re eligible for an extra shot right now.) But what exactly is a booster vaccine? Is it different from a third or extra shot? Does the meaning change if we’re talking about a booster instead of a third dose? To read the full story.