COVID-19 Vaccine
3rd Dose Study

MOSAIC 3: 4th dose (second booster) study
MOSAIC 1: Mix-and-Match of first two doses of approved COVID-19 Vaccines

In 2021 COVID-19 Variants of Concern circulated around the world and there is evidence of some “waning” or decreased effectiveness over time after two doses. Third doses of COVID-19 vaccines have been available in Canada beginning in 2021, and some provinces are providing fourth doses. It is expected that these additional doses will be needed as the virus is will likely circulate in the population for many years.


You can take part in this study if:

  1. You are 18 years of age and older
  2. You are available for all the study visits.
  3. You are in good health with stable health conditions.
  4. You are not pregnant.
  5. You have a record of your previous doses of the authorized COVID-19 vaccines you received.

There are other study criteria that will be reviewed at the first visit to determine if you are eligible or not.

What will I be asked to do?

You will have 1 vaccine dose, 4 clinic visits and 1 telephone/email contact during a 12-month period.  The total time commitment is approximately 2-3 hours.

MOSAIC 2 Study Groups
Randomized GroupsVaccine Dose 1Vaccine Dose 2
Study Vaccine
Dose 4
1bPfizer/BioNTech mRNAPfizer/BioNTech mRNAPfizer/BioNTech mRNA
2bPfizer/BioNTech mRNAPfizer/BioNTech mRNAModerna mRNA
3bModerna mRNAModerna mRNAModerna mRNA
4bModerna mRNAModerna mRNAPfizer/BioNTech mRNA
5bModerna mRNA or Pfizer/BioNTech mRNAModerna mRNA or Pfizer/BioNTech mRNA1Moderna mRNA
6bModerna mRNA or Pfizer/BioNTech mRNAModerna mRNA or Pfizer/BioNTech mRNA1Pfizer/BioNTech mRNA
7bAstraZenecaPfizer/BioNTech mRNA or Moderna mRNA2 Pfizer/BioNTech mRNA
8bAstraZenecaPfizer/BioNTech mRNA or Moderna mRNA2 Moderna mRNA

Previous COVID-19 DosesStudy Vaccine
Dose 4
9b2 doses of any authorized COVID-19 VaccineMedicago VLP

In group 5b and 6b the first and second dose can be either mRNA vaccine as long as they are not the same for both doses.

In groups 7b and 8b the second dose can be either mRNA vaccine.

Participants in group 9b who have completed a primary series (2 doses) of any authorized COVID-19 vaccine, with the second dose administered at least 6 months prior, will be enrolled and receive an unblinded single dose of the Medicago VLP vaccine.