The mixing and matching of COVID-19 vaccines is a dangerous trend and could lead to confusion as not enough data is available on it, the World Health Organization's chief scientist Soumya Swaminathan said on Monday. Canada and some European countries are allowing its citizens to mix and match vaccine doses.

"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, there are studies going on. We need to wait for that" Soumya Swaminathan said in an online briefing.

The scientist added that mixing injections may turn out to be a good approach but one needs to wait. “Maybe it will be a very good approach but at the moment we only have data on the Oxford-AstraZeneca vaccine followed by Pfizer,” she added, reports globalnews.com.

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Canada is among the nations that has allowed the mixing of vaccines. Its  National Advisory Committee on Immunization (NACI) has recommended since June that 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 recommendation, though non-binding, was based on factors such as safety concerns and vaccine supply, said Theresa Tam, Canada’s chief public health officer.

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Several European countries, following safety concerns, have also  recommended that those  who were given a first dose of  AstraZeneca vaccine can  get another vaccine for their second dose. The decision was based on researchers' conclusion  that such mix-and-match vaccination routines were likely to trigger stronger, more robust immune responses.

A study conducted by researchers in Spain had concluded in May this year that vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines produces a potent immune response against the virus SARS-CoV-2.

Early results from the trial of more than 600 people showed the benefits of combining different coronavirus vaccines. 

Booster shots

Speaking about the move by certain countries to administer a third dose of the COVID-19 vaccines, Swaminathan said it will be a chaotic situation if people decide when they should take booster shots.

Stressing the importance of vaccinating citizens, Swaminathan said that there are still countries  where frontline workers have not been vaccinated  and elderly continue to be vulnerable.