You're confusing Astra Zeneca with Pfizer, I believe. AZ is 16W, Moderna is 4W, Pfizer is 3W, J&J is one and done.
Edit:
Link to official Canadian website on Pfizer FAQs
How it’s given
The vaccine is given by an injection (0.3 mL) into the muscle of the arm. For the vaccine to work best, you need to get 2 doses: a single dose and then a
second dose 21 days later.
Immunity develops over time. It takes about 2 weeks to develop significant protection against COVID-19. For the greatest protection, you will need the second dose.
Based on studies in about 44,000 participants, the Pfizer-BioNTech COVID-19 vaccine was 95% effective in preventing COVID-19 beginning 1 week after the second dose.