There is some confusion over the difference between booster shots and third doses of the COVID-19 vaccine, as well as who can get them. We hope to clear up any confusion or misinformation below: What is a third shot? Third shots are offered to people with compromised immune systems 4 weeks after their second dose. Currently, only Moderna and Pfizer recipients can get a third shot. What is a booster shot? Booster shots are generally given 6 months after one's second dose, when