“It’s a little bit of a dangerous trend here. We are in a data-free, evidence-free zone as far as mix and match,” Soumya Swaminathan told an online briefing.
“It will be a chaotic situation in countries if citizens start deciding when and who will be taking a second, a third and a fourth dose.”
Swaminathan later clarified her remarks on Twitter, saying people should follow public health advice and not make their own decisions on vaccine mixing or taking additional doses.
She said public health agencies can provide advice based on available data, but added that studies on mixing various vaccines are ongoing and that “immunogenicity and safety both need to be evaluated.”
In June, the National Advisory Committee on Immunization (NACI) said people who received a first dose of the AstraZeneca vaccine should get an mRNA vaccine — Pfizer-BioNTech or Moderna — for their second dose, unless contraindicated. The vaccines can be safely mixed and matched in most scenarios, they said.
Canadian experts have largely sided with the national agency, recognizing the practice as safe.
NACI also promoted the mixture of mRNA vaccines, saying those vaccines can be interchangeable if the same product was not readily available for the second dose.
That strategy was used in late June in Ontario, when officials promoted the use of Moderna’s vaccine for second doses due to a shortage of Pfizer-BioNTech in the province. Other provinces also took on the recommendation.
The non-binding recommendations were based on a range of factors — from safety concerns to vaccine supply, said Theresa Tam, Canada’s chief public health officer, during a news conference on June 1.
“The interchangeability of vaccines means that you can receive one vaccine product for your first dose and then safely receive a different vaccine for your second dose to complete your two-dose vaccine series for optimal protection from COVID-19,” Tam said.
“This advice provides provinces and territories with effective options to manage their vaccine programs,” she added.
Leading up to the recommendations, Canadian health officials were awaiting studies from Europe that were exploring the mixture of vaccines.
Preliminary results from a University of Oxford study published on May 12 found that mixing the Pfizer-BioNtech and AstraZeneca COVID-19 vaccines may increase the frequency of mild to moderate side effects. But these symptoms were short-lived — lasting no longer than a few days — and there were no hospitalizations or other safety concerns.
Health experts have also stressed in the wake of Swaminathan’s comments that available data shows mixing vaccines is safe and effective, providing a significant immune response against COVID-19.
— With files from Global News