A tale of two COVID-19 vaccines: What is the difference between the Pfizer-BioNTech and Moderna's doses?

The Public Health Agency of Canada has already begun using the Pfizer-BioNTech vaccine to immunize people against COVID-19, and thousands of doses of Moderna are expected to arrive in Canada a matter of weeks.

The two vaccines have shown the best results and went through the common rigorous testing practices that all vaccines do, and have been currently approved for use in Canada, United States and United Kingdom.

How do they work?

Moderna and Pfizer-BioNTech vaccine candidates both operate using the same technology known as messenger RNA (mRNA). While they both sound similar, they are composed of different mRNA molecules and use slightly different delivery systems. The vaccines in essence create spikes that sit on the coronavirus, and when it’s injected into your body, the immune system is able to create antibodies. If someone is then at-risk or has been exposed to COVID-19, the antibodies will be ready to attack the virus and subdue it.

Both the vaccines need to be used twice, with the Pfizer one requiring an injection with three weeks of the original shot and Moderna’s being a month difference.


Moderna’s vaccine efficacy against COVID-19 was 94.1% after the second dose had been injected and did exceptionally well against not only preventing COVID-19, but also limiting it’s severity.

In total, there were 30,000 people involved in the study, with half receiving a placebo. 15,000 that received a saline shot, while another 15,000 received a vaccine and only 11 of them developed COVID-19, and nobody became seriously ill.

Pfizer-BioNTech’s vaccine was 95% effective against COVID-19 after the first dose. With a total of 36,523 participants involved in the study and only 18,198 receiving the vaccine, only eight who received the virus actually tested positive. Much like Moderna’s vaccine, the Pfizer vaccine was also very effective at limiting serious illnesses, with a small portion of trial participants saying at worst they only experienced fatigue or a headache.


Storage becomes a challenge, especially with the Pfizer vaccine which requires storage at temperatures below -70 C. The company has created proprietary packaging so that they can last 10 days without specialized storage, but will ultimately require proper storage.

The Moderna vaccine is a little more forgiving and can last up to 30 days in a common fridge and requires only a -20 C freezer.