Canada’s Chief Medical Officers of Health are now saying it might be OK to delay the second doze of the Pfizer and Moderna COVID vaccines, but only by an additional two weeks. With current constraints in vaccine supply, and the imperative to rapidly vaccinate as many high-risk people as quickly as possible, public health authorities have been examining options, including potentially delaying the second doses of the Pfizer and Moderna vaccines. In a release federal health officials now say, “This option is being considered only when necessary in order to give more high-risk people earlier access to vaccine in jurisdictions where the number of cases are rising rapidly and threatening the health care system’s ability to keep up. Extending the interval between the doses maintains the 2-dose requirement approved by Health Canada while allowing some flexibility to more rapidly protect high-risk individuals and their health care providers in areas with surging COVID-19 cases.”
The National Advisory Committee on Immunization (NACI) advises that while the second dose should be given according to the approved schedule if possible, jurisdictions may consider delaying the second dose due to logistic or epidemiologic reasons until further supplies of the vaccine become available, preferably within 42 days (6 weeks) of the first dose They believe this interval increase is expected to yield similarly high protection seen with second dose administration at 21 or 28 days after the first dose. This is consistent with recommendations released on January 8, 2021 by the World Health Organization that provides flexibility to extend the dose interval up to 42 days in circumstances of vaccine supply constraint and high disease burden.
In a release oday Canada’s Chief Medical Officers of Health indicate they support NACI’s recommendations. “We agree that administration of two doses of the Pfizer and Moderna vaccines must be maintained in line with current evidence and regulatory approvals, and efforts should be made to keep with the manufacturers’ vaccine schedule. The flexibility provided by a reasonable extension of the dose interval to 42 days where operationally necessary, combined with increasing predictability of vaccine supply, support our public health objective to protect high-risk groups as quickly as possible.”