In December 2020, Health Canada approved two vaccines, one from Pfizer (on the 9) and one from Moderna (on the 23). A third vaccine, from AstraZeneca, was approved in Great Britain (December 30). First and foremost, it is important to highlight the extraordinary accomplishment of developing three vaccines.
In the urgent context of COVID-19, governments, scientists, research centres and pharmaceutical companies around the world made a considerable effort to get a vaccine on the market. In December 29, the World Health Organization counted more than 172 products currently being studied in laboratories, 60 of which have already undergone human trials1, bringing a great deal of hope for the next few months. All vaccines have the same goal to trigger an immune response in people against SARS-CoV-2, protecting them before they are exposed to the virus. Vaccines make the body think that it has been infected by the virus (using a modified or copied piece of it), allowing the immune system to prepare to fight off the real thing in the event of infection.
Several different types of vaccines have been tested or are undergoing testing2:
- Vaccines that use the virus itself contain a small quantity of dead virus (like in the flu vaccine) or a weakened version of it (like in the chicken pox vaccine). Viral vector vaccines also contain viruses, but not the same one that causes the disease that the vaccine protects against. Instead, they use viruses that are harmless to humans to deliver part of the virus’s genetic material, or ID card, into our cells. For example, the yellow fever vaccine uses small pieces of other viruses, as does the Ebola vaccine. This is the method used in AstraZenaca’s COVID-19 vaccine.
- Vaccines that use proteins are a more recent innovation and involve injecting coronavirus proteins, which the body can recognize. Examples of this type of vaccine are the whooping cough and HPV vaccines.
- DNA and RNA vaccines are a new type of vaccine and contain no recognizable virus at all. Instead, they bring some of the virus’s genetic material into the body’s cells and tell the body how to make its own “ID cards” for the virus. Pfizer-BioNTech and Moderna used this technique to develop their vaccines with messenger RNA, a piece of the COVID-19 ID card.
In conclusion, the classic vaccine method is to inject an inactive or weakened virus so that the body can learn to defend itself against it. Whereas the messenger RNA technique sends a message to the body in the form of genetic material with information that allows the body to produce an inactive fragment of the virus—a protein—and the antibodies to fight that virus. These antibodies help the body to fight off infection if you ever come into contact with the real virus3.
It is important to note that the messenger RNA vaccine does not use any live samples of the virus that causes COVID-19, so being vaccinated with it cannot give you COVID-19. It also in no way affects or interacts with your DNA.
What are the differences and similarities between the vaccines that have been approved in Canada?
| Company | Pfizer/BioNTech | Moderna |
|---|---|---|
| Type | RNA vaccine | RNA vaccine |
| Efficacy |
95% 94.7% in those over 65 years old |
94.1% 86.4% in those over 65 years old |
| Approved for | People ages 16 and up | People ages 18 and up |
| Number of doses |
Two doses (injected into upper arm muscle): one initial dose and one dose injected 21 days later* Delay may change depending on logistic challenges and data available |
Two doses (injected into upper arm muscle): one Initial dose and one dose injected approximately one month later to a maximum 42 days. Delay may change depending on logistic challenges and data available |
| Side effects |
Typical side effects associated with vaccines At injection site: pain, swelling, redness Rest of body: chills, fatigue, headache Caution: Speak with your health professional about any serious allergies or other health conditions you may have before you receive this vaccine. |
Typical side effects associated with vaccines At injection site: pain, swelling, redness Rest of body: chills, fatigue, headache Caution: Speak with your health professional about any serious allergies or other health conditions you may have before you receive this vaccine. |
For hospital and neighbourhood pharmacists, the challenge is storing the vaccines: the Pfizer/BioNTech vaccine can only be stored in high-performance freezers at between -80 °C and -70 °C, and the Moderna vaccine can be stored for six months at -20 °C and for 30 days at between 2 °C and 8 °C.
Each province has already begun a vaccine rollout in its own established order of priority.
The AstraZeneca vaccine
This vaccine has been approved in Great Britain4 but not yet in Canada. It is a viral vector vaccine, which uses another virus (a chimpanzee adenovirus) that has been modified and adapted to fight COVID-19. This company conducted two studies. In the first study (a half-dose and a full dose one month later), the vaccine had a 90% efficacy. In the second (two full doses one month apart), the efficacy was only 62%. Data is limited on this vaccine’s efficacy in children, adolescents under 18 and people over 65. The vaccine consists of two doses (injected into the upper arm muscle): one initial dose and one dose injected in the fourth to twelfth week after the first dose. It is easy to store, as it can be kept under regular refrigeration, between 2 °C and 8 °C.
COVID-19 vaccines and blood cancer
Currently, no potential vaccine studies have included immunosuppressed subjects (those whose immune systems will have a harder time fighting off infections and illnesses). The efficacy and safety of these COVID-19 vaccines have therefore not been tested in different immunosuppressed populations, such as people with blood cancer5. The risks and benefits of immunosuppressed people receiving the COVID-19 vaccine need to be assessed on a case-by-case basis, depending on the rate of infection in each person’s community. It will also depend on people’s levels of immunosuppression and their underlying reasons for receiving immunosuppressant treatments (including certain cancer treatments). It is therefore highly recommended that you discuss it with your hematologist.
[5] https://www.hematology.org/covid-19/ash-astct-covid-19-and-vaccines