Ask Your Pharmacist

June 30, 2021

I got my first dose of COVID-19 vaccination in April using the Pfizer vaccine. Does it matter if I get the second shot with Pfizer or Moderna?


If you are anything like me, you have had your fill of hearing about anything COVID-19 related. For months now we have been overwhelmed with information about the vaccines available to Canadians. What is even more overwhelming for me, is the speed of the flow of current information, and how quickly the information develops. It is almost too much for me as a health professional to sift through. I imagine for many of us, processing all this vaccine information feels like trying to get a drink of water from a fire hose.

To answer your question, specifically, it does not matter if you get the Pfizer vaccine first and then the Moderna vaccine or the Moderna vaccine and then the Pfizer vaccine. When you received your first immunization, you were likely told that you would be getting the second immunization using the same product you received with the first injection. For example, if you got the Pfizer vaccine for dose one, you were told you would get the Pfizer vaccine for dose two. It is still fine to do this. Similarly, if you got the Moderna vaccine for dose one, it is okay to get the Moderna vaccine for dose two.

Since those early days, more data is available to help guide us about the interchangeability of vaccines. Both Pfizer and Moderna vaccines are mRNA vaccines. According to New Brunswick Public Health, the Pfizer and Moderna vaccines are considered interchangeable. Both are equally effective at preventing severe disease, hospitalization, and death from infection with COVID-19. 

We now also have more data which shows us the importance of getting two doses of immunization, regardless of which vaccine approved by Health Canada is used. Two doses provide much better protection than just one dose against COVID-19 variants, including the delta variant.

Knowing that both Pfizer and Moderna vaccines provide similar protection is important because it puts more vaccine options in the hands of immunizers to provide you with two doses of protection sooner. There are ebbs and flows of vaccine supply into Canada and into New Brunswick. For example, if there is a hold up in Pfizer vaccine supply, we can feel comfortable to go ahead and immunize New Brunswickers with Moderna vaccine even if this is not what was received for a first dose. The same is true with Pfizer, if there is a Moderna shortage.

As of this writing on June 27, the Pfizer vaccine is the only vaccine approved by Health Canada for children aged 12 – 17. It will remain available for both doses to this age group.

If you received a first dose of Astra Zeneca vaccine, and are under 55 years of age, New Brunswick Public Health recommends you get a second dose with either Pfizer or Moderna vaccine in most cases. If you are 55 or older, you can still get a second dose of Astra Zeneca if you choose. 

Fellow New Brunswickers, get the first immunization that is offered to you of the Health Canada approved products, and be sure to follow up with your second dose at the appropriate time interval for you. 

I, for one, very much want to be able to get my mask off and getting 75 per cent of New Brunswickers immunized with two doses of vaccine is something actionable that we can do.  Let’s make it happen.

Dr Kevin Duplisea (PharmD BSc. Pharm, BSc. ACPR) is a pharmacist at Sharp’s Corner Drugstore in Sussex, New Brunswick. His opinions expressed in this newspaper are published for educational and informational purposes only, and are not intended as a diagnosis, treatment or as a substitute for professional medical advice, diagnosis or treatment. Send your questions to