Moderna or Pfizer for Second Doses
As per the National Advisory Committee on Immunization (NACI) guidance, the Pfizer and Moderna
COVID-19 vaccines can be interchanged for first and second doses.
For second doses, the public may not receive the same brand of mRNA vaccine as their first dose,
depending on supply at the local clinic. “Using a different brand of vaccine to complete a vaccine series is
a common practice in routine vaccination for other diseases,” explains Dr. Kit Young Hoon, Medical Officer
of Health at NWHU. “The Moderna and Pfizer vaccines are nearly identical in all aspects and NACI has
said that there is no reason to believe that providing a different mRNA vaccine for a second dose would
result in any additional safety issues or less protection,” Dr. Young Hoon says.
The Delta (B.1.617) variant is more transmissible compared to other variants and having two doses of a
COVID vaccine offers increased protection against this variant. For this reason, getting a second dose of
any mRNA vaccine is very important.
As of yesterday, anyone who had their first dose on or before April 18, 2021, is eligible to get their second
dose. To see other populations who are currently eligible for their 2nd dose, visit
www.nwhu.on.ca/covid19. Anyone eligible for a first or second dose of the COVID-19 vaccine should book
today at www.ontario.ca/bookvaccine.
Dr. Kit Young Hoon
Medical Officer of Health
Northwestern Health Unit