While booster shots are not mandatory, we strongly encourage all our staff to receive booster doses of the COVID vaccine to provide the strongest protection against the Omicron variant. Currently, there is a shortage of Pfizer vaccines in Canada, and as a result, most people over 30 are being offered Moderna only. We are publishing the information below to help you understand why mixed doses have been approved, and what type of protection you can expect after receiving a mixed dose.
Is it safe to mix Pfizer and Moderna vaccines?
Yes, vaccine brands can be mixed.
Both the Pfizer and Moderna vaccines work the same way, and mixing doses has not resulted in any safety concerns (although mild side effects such as chills, headache and muscle pain were reported more frequently in those receiving mixed doses). In an American study published for pre-print in October, boosting with mRNA vaccines (Pfizer/Moderna) resulted in at least two times the number of antibodies for nearly all participants regardless of what brand of vaccine they received for their first and second doses.
Why is Ontario giving out Moderna boosters to people 30+ and Pfizer to people under 30?
Pfizer is being recommended as the preferred vaccine brand for people under 30 due to lower reported rates of myocarditis/pericarditis (heart inflammation) following vaccination with Pfizer as compared to Moderna in this age group. There is no difference in risks between Moderna and Pfizer for people over 30.
Currently, there is a limited supply of Pfizer vaccines across Canada. To make sure there is sufficient supply of Pfizer for 12 to 29 year-olds, most clinics are saving their current supply of Pfizer vaccine for this group.
Is there any difference in protection with mixed vaccine brands?
There is actually preliminary data that shows that mixing COVID-19 vaccines can produce a better immune response. Of note, a major British study published in the Lancet medical journal in December 2021 found that Pfizer /Moderna led to higher antibody and T-cell responses than the standard two-dose Pfizer schedule.