You must wait at least of 21 days before receiving the second Pfizer shot or at least of 28 days before receiving the second Moderna shot. If you miss your appointment for your second shot at 21 days (for Pfizer vaccine) or 28 days (for Moderna vaccine), it’s OK. Those marks are the earliest you can get the second shots. Please make an appointment as soon as possible after that time. It’s important to make sure you get your second shot so you are fully protected and that both shots are the same kind.