Pfizer’s latest data has suggested that a third dose of its COVID-19 vaccine would strongly boost protection against the Delta variant, even more so than two doses alone. 

The unofficial Pfizer data indicates that antibody levels against the Delta variant in those aged 18 to 55 after receiving a third dose of vaccine are higher than for those who have only received their second dose (Howard, 2021). For those aged 65 to 85, the antibody response was even higher (Howard, 2021).

Extra doses in Quebec

The Quebec government is currently offering an extra dose of an mRNA vaccine to those who are looking to travel to countries that don’t recognize their vaccination status (CBC, 2021). As there are certain countries that don’t recognize people as being fully vaccinated if they have received two different COVID-19 vaccines, this has become a concerning issue for the approximate 1.3 million Canadians who have mixed and matched. Health officials have repeatedly mentioned that it is the recipient’s discretion to “seek advice and weigh the risks” prior to receiving a third dose (CBC, 2021).

Robert Maranda, a spokesman for the Health Department states that there are no studies assessing the impact of receiving three doses of two separate vaccines and that “the person should be properly counselled to be informed of the potential risks associated with this added dose compared to the benefits of the planned trip,” (CBC, 2021).

Hope for the immunocompromised

While a third dose may not be recommended for everyone, recent data has shown that it may be beneficial to those who are immunocompromised. According to a world first study, a third dose of the COVID-19 vaccine could provide significantly greater protection against the SARS-CoV-2 virus in transplant patients (Favaro et al., 2021). Because transplant recipients’ immune systems are typically “unable to mount an adequate response to immunization”, they are much more prone to infectious diseases such as COVID-19 (Favaro et al., 2021). As such, the promising results from testing the third dose on transplant patients provides hope for other individuals who are immunocompromised due to other medical conditions.

What are health officials saying?

As of now, there is not enough evidence to demonstrate that a third dose of the COVID-19 vaccine is necessary. In the words of the National Advisory Committee on Immunization (NACI), “there is currently no evidence on the need for booster doses of COVID-19 vaccine after the vaccine series is complete” (CBC, 2021). 

NACI does however recommend that the same mRNA vaccines are used for a second dose, but also ensures that mRNA shots are considered interchangeable should the first type be unavailable (CBC, 2021). Additionally, NACI mentions that any of the approved mRNA options are actually preferred as a second dose regardless of the type of vaccine that was received for the first (CBC, 2021). This is a result of emerging safety evidence and the possibility that having at least one dose of an mRNA vaccine may produce a better immune response (CBC, 2021). 

At the end of the day, it is the individuals’ responsibility to weigh the risks of receiving a third dose. That being said, it would be in your best interest to consult with a primary health physician beforehand in order to make an informed decision.


CBC/Radio Canada. (2021, July 27). Quebec offers extra dose to travellers whose vaccination status isn’t recognized | CBC News. CBCnews.

Favaro, A., Philip, E. S., & Dunham, J. (2021, August 11). Third COVID-19 vaccine dose effective and safe for transplant Recipients: Study. Coronavirus.

Howard, J. (2021, July 28). Pfizer claims 3rd DOSE ‘strongly’ BOOSTS protection against Delta variant. Coronavirus.

About the Author

Bairavie Piravakaran (she/her) is a second-year undergraduate at the University of Toronto Scarborough. As a Psychological & Health Sciences student, she values the importance of sharing credible information and making health resources more accessible to the public. Her interests in population health, research, and design are also reflected in her non-academic pursuits—she currently with the Young Leaders of Public Health and Medicine (YLPHM) as a Social Media Manager for the Scarborough Chapter and is a Health Promotion & Analytics Member at Critical Health Innovations Lab (CHIL). At EMPOWER Health, Bairavie works closely with the Marketing Team in order to plan and execute strategies that help inform the public about current health-related topics.

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