Canada stands by decision to mix and match Covid-19 vaccines despite WHO warning
Canadian health officials have defended their decision to allow the mixing and matching of Covid-19 vaccine doses after a top World Health Organization (WHO) official criticised the practice and called it a “dangerous trend”.
The WHO’s chief scientist Soumya Swaminathan said on Monday, “There are people who are thinking about mixing and matching [Covid-19 vaccines]. We receive a lot of queries from people who say they have taken one [dose] and are planning to take another one. 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 [is concerned].”
Swaminathan clarified her remarks in a tweet, saying, “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.”
But Canada’s health officials stood by the decision to offer second doses that are different from the first.
In an emailed response to queries from HT, a spokesperson for Health Canada and the Public Health Agency of Canada referred to the National Advisory Committee on Immunisation’s (NACI) June 1 on “the interchangeability of authorised Covid-19 vaccines”.
“The NACI reviewed all available evidence from ongoing studies monitoring the mixing of Covid-19 vaccines. The NACI also considered the risk of Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) associated with Covid-19 viral vector vaccines, Canada’s current and projected mRNA (Pfizer-BioNTech or Moderna) vaccine supply and principles of ethical decision-making. Updated recommendations were based on the current evidence and the NACI’s expert opinion,” the spokesperson said.
The spokesperson also said evidence was generated from three studies: the CoM-Cov randomised clinical trial in the UK, the CombiVacS trial in Spain, and an observational study of 326 healthcare workers.
“Current evidence suggests a first dose of the AstraZeneca vaccine followed by a second dose of mRNA vaccine (Pfizer-BioNTech was used in the studies) had a good safety profile,” the statement sent to HT said.
“Evidence on immune responses produced from mixing Covid-19 vaccines was available from the CombiVacS trial in Spain. Current evidence suggests a first dose of the AstraZeneca vaccine followed by a second dose of mRNA vaccine (Pfizer-BioNTech was used in studies) can boost the immune response at shorter (4-week) and longer (8- to 12- week) intervals,” it added.
“Vaccine interchangeability is not a new concept. Similar vaccines from different manufacturers are used when vaccine supply or public health programmes change. Different vaccine products have been used to complete a vaccine series for influenza, Hepatitis A and others,” it noted.
Canada is among a handful of nations where Covid-19 vaccine interchangeability is permitted. That isn’t the case in neighbouring United States.
According to an analysis by the agency Canadian Press, as of July 7, at least 1.3 million Canadians opted for a second dose that was different from the first.
Among those who went for it is Prime Minister Justin Trudeau, who received the AstraZeneca vaccine as his first jab and followed it up with a Moderna mRNA vaccine shot earlier this month.
Canadian guidelines permit not just mixing and matching of the viral vector vaccines like AZ with mRNA jabs, but also between the mRNA varieties.