Paddie Walmsley, 60, and her husband from Coaldale, Alberta, were relieved to receive their first dose of the AstraZeneca COVID-19 vaccine earlier this month. However, their relief is mixed with anxiety as they face a four-month wait for their second shot.
“We’d feel safer and more confident if we could get the second dose sooner,” Walmsley said. Like many seniors, she worries whether the extended interval will leave them adequately protected.
Why the Delay?
In early March, Canada’s National Advisory Committee on Immunization (NACI) recommended extending the interval between COVID-19 vaccine doses from 3–4 weeks to four months due to supply shortages. The goal was to maximize first-dose coverage quickly. Provinces like Ontario, Alberta, B.C., and Manitoba adopted this approach—except in long-term care settings.
But experts argue that a one-size-fits-all strategy may not be appropriate, especially for older adults and immunocompromised individuals.
Elderly at Higher Risk with Delayed Second Dose
Dr. Samir Sinha, a geriatrics specialist at Toronto’s Sinai Health, warns that seniors have weaker immune systems, making them more vulnerable to COVID-19. Delaying their second dose could leave them with waning immunity before full protection kicks in.
Data from the U.K., where doses are spaced 12 weeks apart, suggests that older adults benefit less from a single dose compared to younger people. Immunologist Jörg Fritz from McGill University explains that immunity declines faster in seniors, increasing their risk of infection.
“The worry is that extended spacing may lead to suboptimal immune responses in high-risk groups,” Fritz said.
Vaccine Makers Recommend Shorter Intervals
Both Pfizer and Moderna initially tested their vaccines with 3–4 week intervals, while AstraZeneca’s trials used a one-month gap. Health Canada says NACI is reviewing emerging evidence on extended dosing, but for now, provinces are sticking with the four-month delay.
Derek Phillips, an 82-year-old Toronto resident, was surprised when his second Moderna dose was scheduled 14 weeks after his first—far longer than the originally stated four weeks.
“There shouldn’t be uncertainty about something this important,” Phillips said.
Reinfection and Variants Add to Concerns
A Lancet study found that while most COVID-19 survivors are protected for at least six months, seniors over 65 face higher reinfection risks. Outbreaks in vaccinated long-term care homes—like one in Gatineau, Quebec, where five residents died—raise further concerns.
With more transmissible variants circulating, some studies suggest reduced antibody protection from current vaccines. Fritz recommends booster shots for seniors by winter to ensure strong immunity.
Should Canada Adjust Its Strategy?
Dr. Sinha argues that if the goal is to save the most lives, shortening the second-dose interval for seniors should be considered.
“Older Canadians account for over 95% of COVID-19 deaths,” he said. “We need to prioritize their protection.”
As vaccine supply improves, experts urge policymakers to reassess dosing timelines for vulnerable populations—before more lives are lost.
