Third doses of the COVID-19 vaccine are being administered to different subgroups of people in many countries around the world. The evidence to date supports that third doses of the mRNA vaccines are safe and effective at increasing antibody levels, at least over the short term. To date, additional doses given have used existing vaccines rather than reformulated vaccines (there are several reformulated vaccines currently under study, in an effort to improve the immune response to emerging SARS-CoV-2 variants).
The decision to provide booster doses has been based on the observation that over time there has been a gradual decrease in protection against symptomatic infection afforded by the COVID-19 vaccine. This has been correlated with a gradual increase in infection rates among individuals who are fully vaccinated. This effect has been more pronounced in certain groups, including those who are older in age and those who are immunocompromised.
It is important to note that protection against severe COVID-19—including severe symptoms, hospitalization and death—from the two dose mRNA vaccines or one dose in the case of the Johnson & Johnson vaccine has not significantly decreased over time, and remains very high for the mRNA vaccines.
In Canada, the National Advisory Committee on Immunizations (NACI), an independent group of experts that advises Health Canada, has recently recommended that booster doses of an mRNA vaccine be offered to all long-term care residents and seniors living in other congregate settings, at an interval of at least six months after the primary series has been completed. Additionally, several provinces have begun administering booster doses to higher risk groups, with variation between provinces. For example, in Ontario, booster doses are offered at least two months after the primary series to:
- Transplant recipients, including solid organ transplant and hematopoietic stem cell transplants
- Those undergoing active treatment for solid tumors
- Individuals receiving therapy with an anti-CD20 agent commonly used for conditions such as multiple sclerosis, rheumatoid arthritis, leukemias/lymphoma, etc.
- Those undergoing active treatment with the following categories of immunosuppressive therapies: anti-B cell therapies (monoclonal antibodies targeting CD19, CD20 and CD22), high-dose systemic corticosteroids, alkylating agents, antimetabolites, or Tumor-Necrosis Factor (TNF) inhibitors and other biologic agents that are significantly immunosuppressive
- Individuals receiving active treatment for malignant hematologic disorders, including chemotherapy, targeted therapies, immunotherapy for AML, CML, ALL, CLL, etc.
- Those in receipt of Chimeric Antigen Receptor (CAR)-T-cell
- Those with moderate or severe primary immunodeficiency, such as DiGeorge syndrome and Wiskott-Aldrich syndrome
- Stage 3 or advanced untreated HIV infection and those with AIDS
In the USA, the Food and Drug Administration (FDA) recently authorized booster doses for the Pfizer-BioNTech vaccine for:
- Individuals 65 years of age and older
- Individuals 18-64 years of age at high risk of severe COVID-19
- Individuals 18-64 years of age whose frequent institutional or occupational exposure to SARS-CoV-2 puts them at high risk of serious complications of COVID-19, including severe COVID-19
As new research emerges regarding the effectiveness of the COVID-19 vaccines over time and impact of booster doses, it is anticipated that the recommendations regarding receiving extra vaccine doses will change to reflect the growing scientific understanding.
Coinciding with the granting of full authorization by the US Food and Drug Administration (FDA) and by Health Canada, the vaccine manufacturers are now legally allowed to market the vaccines using brand names. It is important to note that there has been no change in the vaccines themselves, and that the only change is to the label, which now incorporates a brand name in addition to the generic name.
The vaccine brand names are as follows:
- Pfizer-BioNTech vaccine: Comirnaty
- Moderna vaccine: Spikevax
- AstraZeneca vaccine: Vaxzevria, Covishield
- Johnson & Johnson vaccine: no brand name to date
Over the past several months, every Canadian province has announced plans to implement proof of vaccination programs, otherwise known as “vaccine passports”. This program has already come into effect across much of the country. While there are some differences in the precise implementation between provinces, it is generally the case that all individuals 12 years and older will be required to provide proof of vaccination to access non-essential settings (e.g., restaurants, clubs, sports venues, movies, gyms), but such proof would not be required for access to essential services (e.g., grocery stores, religious settings, personal service facilities). Proof of vaccination may be an electronic credential or a paper copy of a vaccination receipt (depending on the province and the stage of implementation). The programs generally provide an exemption for individuals who are medically unable to receive the COVID-19 vaccine. Since unvaccinated individuals are responsible for a disproportionate amount of the spread of COVID-19 at this time, implementation of these programs will help to reduce the risk of transmission in settings where proof of vaccination is required.
The Mu variant is a strain of SARS-CoV-2 that was first identified in Colombia in early 2021. Since then it has spread to many countries around the globe. The Mu variant has been classified as a “variant of interest” by the World Health Organization, because it has mutations that are associated with the potential for reduced vaccine effectiveness—there has been evidence that antibodies formed against other SARS-CoV-2 strains may be less able to neutralize the Mu variant. Despite the concern about this variant, it is important to note that apart from Colombia and Ecuador, the prevalence of the Mu variant remains very low (i.e., less than 0.5 per cent of cases in Canada). The Delta variant remains the predominant strain across both Canada and the U.S. at this time.