Canadians will receive one of two COVID-19 vaccines: the first developed by Pfizer-BioNTech and the second by Moderna. There are minor differences, but both are more than 94% effective at preventing infection by the SARS-CoV-2 virus.
The Pfizer-BioNTech vaccine has shown to be 95% at preventing symptomatic COVID-19 infection, starting seven days after administration of the second dose. The Moderna vaccine is 94.1% effective at preventing symptomatic Covid-19, starting from 14 days after the second dose. Both vaccines also appear to reduce the risk of severity and complications in those infected with COVID-19.
Both of the vaccines require cold storage to maintain effectiveness. Pfizer’s is the more difficult to store stably, requiring shipping and storage in ultracold freezers that can maintain temperatures of –70°C. Moderna’s needs to be frozen, too, but at –20°C; closer to the temperature of a regular freezer. After thawing, a vial of the Pfizer vaccine must be used within five days. Moderna’s can remain stable at fridge temperature for 30 days, and at room temperature for 12 hours.
How the vaccines work
Both vaccines are Messenger RNA (mRNA)-based. These vaccines work by “teaching” cells to create a spike protein – similar to that found on the surface of the virus that creates COVID-19 – triggering an immune response without any exposure to the live virus. This in turn causes the body to produce antibodies to fight off infection. But the main benefit of mRNA vaccines, like all vaccines, is that vaccinated individuals gain protection without risking the consequences of infection.
Both the Moderna and the Pfizer-BioNTech vaccines require two shots: a priming dose, followed by a booster shot. The interval between Moderna doses is 28 days; for the Pfizer vaccine, it’s 21 days.
While many vaccinated individuals feel nothing at all, both vaccines have the potential to cause minor side effects. The vast majority of these are mild and similar to other vaccines, clearing up within 24 hours: injection site pain or minor swelling, fatigue, light fever, headache, muscle pain and joint pain. These aren’t signs the vaccine is unsafe, however. Rather, they mean the immune system is kicking in.