The National Advisory Committee on Immunization (NACI) suggests that COVID-19 vaccine types should remain consistent. They released this in a set of recommendations on May 21.
They say that your first and second doses of the vaccine should be of a similar type.
So for example, if you received a Pfizer or Moderna “M-RNA” type vaccine they suggest that your second should not be mixed with either an Astrazeneca or Johnson & Johnson Vaccine, or vice versa.
They say there is no reason you shouldn’t be able to interchange brands within each type, so a Pfizer for your first and a Moderna for your second should be okay. But no data currently exists to support that.
And if your first shot was an Astrazeneca and you’re unable to receive a second dose of it due to restrictions, they say you can receive the Johnson & Johnson Vaccine to supplement it.
Currently, both Astrazeneca and Johnson & Johnson vaccines are on hold. Astrazeneca for blood clotting issues that have arisen in some recipients, and Johnson & Johnson for a tainted batch issue.
They say further information on this is expected in June.