‘More than a booster': Third dose is our best defence against the COVID-19 Omicron variant, says Dr. Jeff Powis

When Dr. Melinda Hillmer received her third dose of the COVID-19 vaccine on November 8, 2021, she did not anticipate the sense of urgency that would follow only a few weeks later.

Not only did Ontario confirm its first two cases of Omicron – now the dominant COVID-19 variant in the province – but her entire family, including her three children and husband, tested positive for the COVID-19 Delta variant.

Three COVID-19 doses critical to the fight against Omicron

Like many parents and families, Dr. Hillmer, a staff physician in Michael Garron Hospital’s (MGH) Medicine Department, was looking forward to getting her eight-year-old and 11-year-old children vaccinated.

However, after one child was exposed to the COVID-19 Delta variant, the infection quickly spread to her other two children and husband, and put the family’s vaccination plans on pause. 

Dr. Hillmer was the only one in her family not infected with COVID-19. She was also the only one that had three doses of the COVID-19 vaccine.

New evidence suggests that the transmissibility of Omicron in Canada is much greater than the Delta variant. Recent data released by the Ontario COVID-19 Science Advisory Table shows the reproductive rate (R value) for Omicron at 4.01; comparatively, the Delta variant has an R value of 1.09.

“The reproductive rate of the Omicron variant is unprecedented in this pandemic; we have never reached numbers this high,” says Dr. Jeff Powis, Medical Director, Infection Prevention and Control (IPAC) at MGH.

“When Ontario released the COVID-19 vaccine passport acknowledging ‘full vaccination’ as two doses, we were going off of the best evidence we had at the time – but we know that information continues to evolve so we need to be adaptable to keep our communities safe. Therefore, we should be thinking of the third dose of the COVID-19 vaccine as more than a booster – but rather as a third dose in the COVID-19 vaccine series.”

Dr. Powis strongly encourages all eligible Ontarians to get their third dose of the COVID-19 vaccine as soon as possible to reduce severity of illness, hospitalization and mortality due to the virus.

Research and real-world data show that a third dose of an mRNA vaccine – either Pfizer or Moderna – offers strong protection against Omicron, regardless of what vaccine brand you received for your first and second doses.

“It is safe and effective to mix vaccine brands, especially for your third dose. What’s most important is the additional protection that a third dose provides,” Dr. Powis says. “Whether that vaccine is Pfizer or Moderna, both will provide you maximum protection against COVID-19, including the Delta and Omicron variants.”

Get Your first, second or third dose of the COVID-19 vaccine today

• Book an appointment using the provincial booking system online or by calling 1-833-943-3900
• Book an appointment at a participating pharmacy
• Walk in to one of MGH/ETHP's mobile and pop-up clinics. Please read the eligibility carefully for these clinics.