Why Canada’s decision to delay 2nd doses of COVID-19 vaccines may not work for everyone

Small, pre-print study suggests elderly among those who may benefit from quicker timeline

Adam Miller · CBC News · Posted: Mar 27, 2021

People wait in line to receive their COVID-19 vaccination at a clinic in the Fraser Health region of Surrey, B.C., on Wednesday. New early data suggests that Canada’s recommendation to delay the second dose of COVID-19 vaccines for up to four months may not be effective in some older, more vulnerable people.(Ben Nelms/CBC)

[Excerpts] New research from two small pre-print studies suggests delaying second doses of COVID-19 vaccines by up to four months may not be the best approach for some older Canadians.

The research comes as some experts are also questioning whether Canada’s vaccination advisers, who recommended the delay, can keep up with rapidly evolving science during the pandemic.

Prior to the pandemic, the National Advisory Committee on Immunization (NACI), which has provided guidance to the federal government on vaccinations since 1964, met just three times a year to discuss issues related to vaccines for influenza, mumps, measles and other viruses.

But a year after the pandemic was declared, with new data emerging daily, NACI has been thrust into the spotlight and forced to evaluate new vaccines for a novel virus faster than ever before.

“NACI’s committees are basically made up of volunteers, many with heavy daily responsibilities during the pandemic,” said Dr. David Naylor, co-chair of Canada’s COVID-19 Immunity Task Force.

“There’s no precedent for NACI to operate at this pace, and everyone is adapting on the fly.”

NACI has met nine times since Canada approved its first COVID-19 vaccine on Dec. 10, but it has plans to ramp up in the coming months with another 13 meetings scheduled between now and the end of June.

The committee has previously overturned its initial guidance against immunocompromised individuals and pregnant women receiving COVID-19 vaccinations, as well as a controversial decision against the AstraZeneca-Oxford vaccine for those over 65.

Delay could leave cancer patients less protected, U.K. study suggests

A new pre-print study, which has not yet been peer reviewed, analyzed 151 older cancer patients and compared their immune response with 54 healthy adults after receiving the first and second doses of the Pfizer-BioNTech COVID-19 vaccine in the U.K.

  • Benefits and risks of delaying 2nd doses of COVID-19 vaccine

    The researchers concluded that delaying second doses to between eight and 12 weeks for most cancer patients left them “wholly or partially unprotected” and had implications on their health and the potential emergence of coronavirus variants. 

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The decision was also informed by findings from Dr. Danuta Skowronski, epidemiology lead at the British Columbia Centre for Disease Control (BCCDC), who determined that one dose of the vaccine was actually more effective than clinical trials had initially shown.

NACI said if second doses were stretched to four months across the country, close to 80 per cent of Canadians over the age of 16 could get at least one shot by the end of June.

But Canada’s chief science adviser, Mona Nemer, has said the decision to delay second doses amounted to a “population level experiment” and advised against the delay in older Canadians on CTV’s Power Play this week, citing a lack of data to back up the decision.

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“Now, in certain populations — older people, people with comorbidities and cancers — likely delayed boosting for them is sub-optimal and possibly will lead to revised recommendations for those groups.”

B.C. study analyzed long-term care residents

A second pre-print study released this week from researchers in British Columbia, which has also not been peer reviewed, cast further doubt on the dose delay for seniors and found that their immune response may not be as strong as in younger, healthier people.

The study analyzed antibody levels in a dozen long-term care residents in Vancouver a month after receiving their first dose of a COVID-19 vaccine, compared with 22 younger health-care workers — 18 of whom had not previously been infected by COVID-19 and four who had.

“The level of antibodies in older residents was fourfold lower, so significantly decreased,” said Dr. Marc Romney, a clinical associate professor at the University of British Columbia in Vancouver and one of the authors of the study. “The function of those antibodies in older people was also compromised.”

Romney said antibodies are just part of the picture, and he also plans to look at the immune system’s full response in future research. But he said the fact that antibodies in the elderly didn’t neutralize the virus as well as in the younger health-care workers suggests the dose delay may need to be revised for them.

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