OTTAWA, ON – Canadians who got a first dose of the AstraZeneca COVID-19 vaccine can now get a Pfizer or Moderna shot as a second dose. 

Ottawa has given the green light to mixing vaccine schedules based on new guidance from the National Advisory Committee on Immunization. 

If your first dose was the AstraZeneca or COVISHIELD vaccine you can still receive a second dose of those. In addition, Moderna and Pfizer shots can be used in first and second-dose combinations safely.

“The interchangeability of vaccines means that you can receive one vaccine product for your first dose and safely receive a different vaccine for your second dose to complete your two-dose vaccine series for optimal protection against COVID-19,” says Chief Public Health Officer, Dr. Theresa Tam.

The new advice comes in light of recent studies from Germany, the UK and Spain on the safety of using mixed COVID-19 vaccines.

Tam says one those studies, from Spain indicates that mixing vaccines, like AstraZeneca and Pfizer, actually produces an even more robust immune response.

There could be more side effects however. A U.K. study reported in May that mixing AstraZeneca and Pfizer led to more reports of fevers and fatigue, but those were short-lived. This study, like the Spanish one, also concluded mixing the two for first and second doses was safe.