Extension of Second Dose Intervals for COVID- 19 Vaccines

Ontario government is extending the vaccination dose interval up to 16 weeks for the three two-dose vaccines currently approved by Health Canada (Pfizer-BioNTech, Moderna and AstraZeneca/COVISHIELD). This is based on the recommendation of the National Advisory Committee on Immunization (NACI).

Individuals who have already booked their second dose will have their appointments rescheduled.

This will allow Ontario to rapidly accelerate its vaccine rollout and maximize the number of people receiving first dose within a context of limited supply.

Current evidence from research and real-world experience have shown that even with a single dose of the vaccine, there is protection from severe complications, hospitalization and death due to COVID-19. For ongoing protection, a second dose will still be necessary after 4 months.

Clinical trials with the AstraZeneca/COVISHIELD vaccine indicate that vaccine efficacy increases with the length of the interval between doses over 12 weeks.