U of G scientists concerned about extended interval between COVID-19 vaccine doses

Bridle: 'Science relies on empirical data and there is no data to prove the four-month interval will work'

GUELPH – A group of virologists and immunologists at the University of Guelph wants the provincial government to put the brakes on its directive to extend the period between doses of the Pfizer and Moderna COVID-19 vaccines to four months.

It’s not that there’s anything wrong with the vaccines, said Dr. Byram Bridle, a viral immunologist in the department of pathology.

“We very much promote vaccination,” he said in an interview on March 18.

“As scientists, we are simply trying to say, follow proper scientific protocols. Science relies on empirical data and there is no data to prove the four-month interval will work.”

Bridle, virologist Dr. Sarah Wootton and immunologists Dr. Bonnie Mallard and Dr. Neil Karrow have written a letter “to Canadians,” outlining what they as scientists, view as pitfalls in the decision to change the dose interval without evidence.

“Specifically, we have been advocating for the administration of safe and effective COVID-19 vaccines according to the protocol that was used to have them approved for emergency use, until further data is available and reviewed and approved by Health Canada to support alternative protocols,” the letter reads.

“The intervals for the two-dose COVID-19 vaccines should adhere to what was officially approved by Health Canada and the manufacturers, which is 21 and 28 days for the Pfizer and Moderna vaccines, respectively.”

Bridle said the idea of extending the interval between doses seems to have originated from a letter to the editor of The New England Journal of Medicine published on Feb. 17 claiming that a single dose of the Pfizer vaccine is 92% effective.

Danuta Skowronski at the British Columbia Centre for Disease Control in Vancouver, and Gaston DeSerres at the Institut National de Santé Publique du Québec, explained their theory in the letter and their belief that with 92% efficiency, it is better to get first shots to more people and circle back with the booster in four months.

There’s all kinds of wrong with that, Bridle said, including that the numbers used were too small to be statistically significant and that the entire claim “comes from extrapolation of data that was never designed for this type of analysis.

“But they took the Pfizer data, put a subset into an epidemiological model, asserted scientific assumptions and extrapolated from that the idea that a single dose is 92% effective,” he said.

Pfizer responded to the letter to the editor, stating its own data suggests a single dose might be 50% effective and that they have not studied the long-term efficacy of a single dose, nor the impact of extending the period between first and second doses.

“And yet the NACI (National Advisory Committee on Immunization) has taken that data and mandated it into practice,” Bridle said.

He added if the assumptions are wrong in the first place, delaying the booster shot could just as easily provide little protection and leave time for the SARS-CoV-2 virus to mutate, rendering useless the vaccines that have been developed.

“In science we don’t just jump into the unknown like that,” said Bridle.

“The company has to hold phase three clinical trial testing, submit it, and then be approved by Health Canada.

“And Health Canada hasn’t approved the four-month interval.”

Bridle said he and his colleagues have reached out to the NACI and to the province and are awaiting a response.

Several other scientists, including Canada’s chief science adviser Dr. Mona Nemer, have also spoken out against extending the time between doses, noting it can have a negative effect on efficacy, notably in seniors.

Recent research out of the U.K. indicates 95 per cent of cancer patients produced an antibody response if they received the second Pfizer vaccine dose three weeks after the first, while just 43% of patients showed the same response with five weeks between doses.

Other experts have argued spacing the doses father apart is a good way to lower infections and to prevent new variants from emerging.

Regardless, on March 8, Dr. David Williams, chief medical officer for Ontario, sent letters to all the medical officers of health in the province directing them not to schedule second appointments and to extend the interval between shots to four months.

Danny Williamson, spokesperson for Wellington-Dufferin-Gueph Public Health, says the health unit is following the advice of NACI and takes direction from the province’s chief medical officer of health.

“In terms of the consent question, nurses obtain consent before providing each individual dose of vaccine and not for vaccine series,” he said in an email.

“We will continue to monitor the best evidence available on COVID-19 vaccines and adhere to the guidance of the Chief Medical Officer of Health as current. As vaccine supply increases locally or as new evidence becomes available, the need for a longer interval will continue to be re-evaluated by both NACI and the province.”

Anti-vaxxers will never be convinced, but Bridle’s biggest fear is that those who are vaccine hesitant may decide not to get the vaccine because of the conflicting information.

And it’s not just the COVID-19 vaccine at stake, he said, but potentially all vaccines.

“We don’t want people losing faith in vaccines,” he said.

“They are the ultimate form of medicine and the cheapest, most effective way of treating disease, as long as they are proven safe and used in the proper way.

“If people lost faith in the Canadian application of the COVID vaccine, maybe they will do that with other vaccines too.

“We don’t want parents to stop getting their children vaccinated.”