You must wait at least 21 days before getting the second dose of the Pfizer vaccine or 28 days before getting the second dose of the Moderna vaccine. For both vaccines, you should wait no longer than 6 weeks (42 days) between doses.  You will be asked to sign up for your second vaccination dose when you get the first one and the scheduler will help make sure the correct number of days pass between vaccinations. It is important to make sure you get your second dose, so you are fully protected and that both doses are the same kind of vaccine. If more than 42 days have passed since your first dose, you should still get your second dose as soon as possible.  The Centers for Disease Control and Prevention do not recommend getting a third dose if you fall outside of this time frame. For more detailed information, visit https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html.