TORONTO —
Experts in Canada say that comments by the World Health Organization’s chief scientist on mixing and matching COVID-19 vaccine doses have been taken out of context and that doing so under public health guidelines is safe and effective.

The WHO’s Dr. Soumya Swaminathan said during an online briefing Monday that there is little data on mixing and matching vaccines and that it could be a “chaotic” situation if “citizens start deciding” when they should be taking “a second or a third or a fourth dose” and from which vaccine manufacturer.

“To be charitable here, I think this was a conversation that was taken out of context,” Dr. Sumon Chakrabarti, an infectious disease doctor, told CTV News Channel on Tuesday.

In some parts of the world, he said, people have taken it upon themselves to get multiple doses of various COVID-19 vaccines so they can travel.

“We’re seeing in other parts of the world, some people are getting a certain vaccine, say Sinopharm – not available in Canada — and then trying to get another two doses of vaccine to get double vaccinated or get a vaccine that will satisfy some sort of condition,” he said.

Some countries will not allow travellers to cross their borders without full vaccination via specific authorized vaccines. Others, including Canada, require travellers to quarantine for 14 days unless they’ve been fully immunized with one of the vaccines authorized for use in the country.

In a statement to CTVNews.ca, the WHO said that Swaminathan’s remarks were targeted towards individuals.

“At our Global press conference on COVID 19, Dr. Soumya Swaminathan explained that individuals should not decide for themselves, public health agencies can, based on available data. Data from mix and match studies of different vaccines are awaited – immunogenicity and safety both need to be evaluated,” the statement said.

In Canada, the National Advisory Committee on Immunization (NACI) and Public Health Agency of Canada have said mixing and matching doses is safe based on available evidence. In a June update to COVID-19 vaccine recommendations, NACI said that the mRNA vaccines can be used interchangeably if the original dose is not available, and that a second dose of mRNA vaccine is recommended for those who got AstraZeneca as a first dose.

“I agree that mixing and matching doses of vaccine is safe, we have evidence for this, we’ve been doing it, and it works so I think that that discussion was something that was not applicable to what’s happening in Canada,” Chakrabarti added.

Studies conducted in other countries have shown that mixing mRNA and AstraZeneca vaccines can promote a stronger immune response.

“We have some evidence out of Spain, in England, and also Germany showing that you can actually put these two vaccines together, and you see actually a boost in the amount of antibodies you get,” he said.

Canadian researchers are conducting their own study on mixing and matching vaccines. The study will investigate the impacts of the use of COVID-19 vaccines from different manufacturers in adult participants.

Dr. Joanne Langley, co-principal investigator of the MOSAIC study and infectious disease physician, told CTVNews.ca in a phone interview on Tuesday that the Canadian study is investigating antibody responses to mix-and-match vaccine schedules and will document how participants are feeling in the short-term and long-term.

Due to Canada’s quickening vaccine rollout, the researchers have run into issues getting enough participants for the study, particularly as it also aims to examine extended intervals of up to 70 days between doses.

“They think they can get it quicker through public health and that may not be the case,” Langley said. “There is an interval so you can get it as soon as 28 days from your first vaccine or as long as the 70 days, but if you’re already at two months from your first vaccine that means it’s only two weeks to get your next one.”

The study is done in conjunction with the COVID-19 Immunity Task Force, Vaccine Surveillance Reference Group, Canadian Immunization Research Network and Dalhousie University and it will investigate mixing and matching vaccines and extended dose intervals in 1,300 adults across Canada at Canadian Immunization Research Network clinical trial sites. These sites are located in Nova Scotia, Quebec, Ontario, Manitoba, Alberta and B.C.

And while Langley agrees that there is room for more data and evidence, there are currently at least 26 studies on mixing vaccines being conducted worldwide. She too thinks Swaminathan’s remarks were taken out of context.

“She was referring in particular to what some people are talking about doing: getting a third and a fourth dose, and that absolutely should only be done if it’s recommended by public health people,” she said. “In Canada you couldn’t do that. But in some countries, you could access the vaccine as an individual.”

COVID-19 vaccines aren’t the only ones we see mixed and matched with other brands. This happens with other vaccinations that Canadians need occasional boosters for.

“We also know from previous vaccines, outside of COVID, that this works,” Chakrabarti said. “For example, with pneumococcal vaccinations, this is something that’s safe.”

In a statement to CTVNews.ca, the Public Health Agency of Canada also said that vaccine interchangeability happens regularly in Canada.

“Vaccine interchangeability is not a new concept. Similar vaccines from different manufacturers are used when vaccine supply or public health programs change. Different vaccine products have been used to complete a vaccine series for influenza, hepatitis A, and others,” the statement read.

The WHO’s latest messaging may have also been an attempt at stopping countries from hoarding COVID-19 vaccines for future booster shots, one infectious disease doctor said.

“I do sincerely believe that it was a well-intended message aimed at preventing the idea of hoarding too many doses of vaccines for booster shots, and potentially third or even fourth doses, especially when you’re dealing with a situation where COVAX has not worked ideally for under resourced parts of the world,” Dr. Abdu Sharkawy told CTV’s Your Morning on Tuesday.

Swaminathan did caution on Monday that “if 11 high and upper middle income countries decide… that they will go for a booster for their populations or even subgroups, this will require an additional 800 million doses of vaccine.” She said that would affect the global vaccine supply at a point “when there is no scientific evidence to suggest that boosters are definitely needed.”

Despite good intentions, Sharkawy said that he was surprised that Swaminathan said mixing and matching COVID-19 vaccines was an “evidence free zone,” as studies around the world have yielded evidence and real-world evidence is taking place.

“When you’re talking about the science behind this protocol, and we’re dealing with emerging real-world evidence from multiple parts of Europe, that shows that this is a safe and effective strategy to use,” he said. “So for any Canadian who did receive a multi-platform vaccine protocol, including my own wife, I say you have nothing to fear. The science is very sound.”

For those who did mix their vaccine doses, Langley said they did the right thing by following public health advice and that advice hasn’t changed.

“The most important thing is to have two doses of an authorized COVID vaccine, so that you will reduce your likelihood of getting COVID serious complications,” she said.

For Chakrabarti, he has no doubt in the safety of mixing and matching and even recommended his own father mix doses.

“I wouldn’t do that unless I thought it was entirely safe.”

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