A national panel of experts is continuing to recommend that second doses of COVID-19 vaccinations can wait up to four months, a position that places Canada among countries with the longest delays between shots.
The National Advisory Committee on Immunization (NACI) provided the guidance Wednesday in a 41-page report, saying current evidence shows that a single dose offers good protection and will “allow faster population-level protection” that would thwart the spread of the virus. At the same time, the committee’s report said it anticipates that most people will not have to wait that long as supplies ramp up.
The four-month recommendation was first made last month. The country’s public-health officers sent out a statement Wednesday saying that the population benefits of the four-month delay outweigh individual risk. Canada currently only has enough vaccines to offer first-dose coverage to just more than one-quarter of the population.
“A number of countries are using three-months intervals. I think Canada might be the only one using a four-month interval,” said Shelley Deeks, a communicable-disease specialist and NACI vice-chair. “But we’ve emphasized our recommendation is up to four months. What we are expecting to see as the provinces and territories roll out programs is that this period of time can actually decrease as more and more people are getting vaccinated.”
The U.S. Centres for Disease Control has said second doses can wait up to 42 days. In Britain, second doses can be administered up to three months after the first.
Eleanor Fish, a professor of immunology at the University of Toronto, said accumulating evidence shows that Canadian vaccination campaigns should stick to the manufacturers’ recommended schedules of three or four weeks between doses, at the very least for people more than 55 years old and those who are immunocompromised.
With the four-month gap, “we’re really talking about partial protection, which we don’t know how long it will last,” Dr. Fish said. “But the point is, when you get a second dose within the time frame the trials examined, there is no question you get an excellent response.”
The NACI recommendation has real-world consequences for vulnerable people anxiously awaiting a second shot.
On Wednesday afternoon, Pina Rotilio met her parents, Frank and Maria Menniti, on the front stoop of their Toronto home to deliver their grocery supply. The couple received a first dose of vaccine March 10 but second doses scheduled for April were cancelled.
Mr. and Mrs. Menniti, aged 95 and 89, respectively, cancelled home care to avoid the risk of infection when the pandemic began. Mrs. Menniti does the heavy lifting around the house, despite arthritic hands. Mr. Menniti used to get home care to help him shower but Mrs. Menniti does it now. She turns 90 next week.
“I feel very lonely. I’m so tired,” Mrs. Menniti said. “I’d really like to get that second vaccination and have my daughter come and help me. I can’t do it any more. My husband can’t do nothing. Nobody can come inside.”
Their daughter, Ms. Rotilio, will get her first shot on the weekend, but nobody feels comfortable mixing indoors until her parents have two doses.
“We would still wear masks to protect them, but if they were fully vaccinated, I think we would be okay with partially vaccinated caregivers,” Ms. Rotilio said.
Mr. and Mrs. Menniti received the Pfizer-BioNTech vaccine. The NACI summary of the evidence for people more than 70 says that the vaccine showed anywhere from 58-per-cent-to-63-per-cent efficacy at preventing symptomatic illness and are 65 per cent to 83 per cent effective at preventing hospital admissions after one dose. There was no breakdown for 90-year-olds.
Dr. Fish points out that the Pfizer and Moderna vaccines are different than traditional antibody vaccines that often provide good protection after one dose. The new vaccines require a prime and booster to get to full protection.
She is also concerned, she said, that partial immunity might encourage the development of new variants.
Preliminary studies have recently questioned whether a single dose offers sufficient immunity to the elderly and cancer and transplant patients. The NACI recommendation took note of those studies, but added that there is limited “efficacy data on two-dose series in those populations” because they were not included in clinical trials.
Dr. Fish emphasized, however, that no clinical trials prove the efficacy of a four-month gap, either. The vaccine companies will soon release information on how long immunity lasts. “Importantly, Canada will have to examine the longevity of the response to this revised dosing schedule, in terms of when we give a booster, as we have not followed protocol,” she said.
Ontario has given second doses to all nursing-home residents but not the elderly outside care settings. Other provinces, such as Quebec and British Columbia, have generally only given single doses so far.
Ontario followed the recommendations of its own Vaccine Clinical Advisory Group to stick to the manufacturers’ recommended dose intervals of three to four weeks for some immunocompromised people, including transplant and some cancer patients. It recommended extending second doses for the elderly outside care settings.
The NACI report said growing vaccine stockpiles should allow provinces to shorten the delay. “Every province can modulate second doses according to their supplies, and shorten the interval for older people,” said NACI chair and infectious-disease specialist Caroline Quach-Thanh. “But for now, the data is reassuring.”
With a report from Tijana Martin
Sign up for the Coronavirus Update newsletter to read the day’s essential coronavirus news, features and explainers written by Globe reporters and editors.