For the most part, if you got the Pfizer mRNA vaccine for your first dose, you will get Pfizer again for your second dose. If you got the Moderna mRNA vaccine for your first dose, you may get either Moderna or Pfizer for your second dose. The Pfizer and Moderna mRNA vaccines are safe to mix.
If you received the AstraZeneca vaccine for your first dose, you can pick AstraZeneca, Pfizer or Moderna, depending on what is available, for your second dose. There are no safety concerns with getting a Pfizer or Moderna vaccine as your second dose.
You are likely to experience milder side effects if your second dose is the same type of vaccine as the first dose. If you have questions, please talk to a member of your health care team.