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Mixing COVID-19 vaccines may have more than one benefit: Infectious disease expert

Dr. Lisa Barrett says the evidence available points to it being better and more effective to get mRNA for the first COVID-19 vaccine dose and another type of vaccine for the second.

Canadian scientists are joining their counterparts around the world, as they undertake clinical trials to see if different COVID-19 vaccines can work together. 

"We don't have the answer yet and we need to do that experiment," says Dr. Lisa Barrett, infectious diseases physician and researcher, Dalhousie University. "Why would you even bother to do that type of experiment? Well, for two reasons: number one, we know that there are shortages and differences in when vaccines are available; and number two, based on other vaccines, using different vaccines might actually work very well from an immune system's perspective."

Dr. Barrett tells CityNews' The Rob Snow Show, mixing vaccines is safe for the most part. Scientists just want to make sure immune response, regarding both the antibodies that one makes from the vaccine and the other parts of the immune system that respond to viruses, provide the same amount of defence against COVID-19 compared to only using one type of vaccine for both doses. 

So far, she says the evidence available points to it actually being better and more effective to have taken doses of different vaccines.

"Let me put it this way, the first dose is your high school education and the second dose is your university education," Dr. Barrett says. "If you go between the mRNA vaccine [like Pfizer BioNTech and Modern] as your first dose and then a different type of vaccine like Astra-Zeneca or Johnson & Johnson for your second, its like your immune system is taking its knowledge of the virus to the next level instead of repeating the same process." 

However, until clinical trials reveal whether the vaccines work well together, public health officials aren't allowing people to mix and match, but news is expected to come soon.

The infectious disease expert says, if mixing vaccines is possible, it would at the very least help with the vaccine rollout and distribution as supplies are still unstable for the short-term. 

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