Quebec is planning to use a different vaccine for the 2nd dose in some cases. Here's what the experts say

Jonathan Marchand, a resident of a long-term care home north of Quebec City,got his first dose of a COVID-19 vaccine back in December and he's getting a second dose on Friday.

But it won't be from the same company.

"I would have preferred to have received the Moderna vaccine, which was the first dose I received, but I'll take the Pfizer one. It's almost the same,"said Marchand, a 44-year-olddisability rights activist.

Marchand isn't the only one who will be getting a vaccine cocktail.

Quebec is planning to administer second doses to the province's most vulnerable residents even if the second dose doesn't match the first.

A single dose can provide ample protection to mostbut seniors are particularly susceptibleto the disease.And just asit's time to boost their protection, Modernadeliveries have been significantly delayed by"quality assurance" backlogs.

So health officialsare wading into relatively uncharted territory by using a different mRNA-based COVID-19 vaccinewhilestudies on the effectiveness and safety of combining the two are still underway.

On the surface, this may sound like a gamble, but some experts sayit would be riskier to delay the second dose while more transmissible variantsof the coronavirus are spreading through the province.

WATCH |Doctor explains what could happen if you mix COVID-19 vaccines:

What could happen if you mix COVID-19 vaccines?

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Dr. Donald Vinh, an infectious diseases expert at the Research Institute of the McGill University Health Centre, explains the three possible outcomes of mixing your first and second doses.

Dr. Donald Vinh, an infectious diseases specialist at the McGill University Health Centre who wasalso a science adviser for the federal COVID-19 therapeutics task force, said it all comes down to a race against the variants.

Even if the second dose is different from the first, he said, "there is undoubtedly going to be some level of protection that is going to be given or enhanced."

Vaccine combo could mean stronger immunity: Arruda

Some vaccinologists suspect that getting a different type of COVID-19 vaccine for the second dose could stimulate immune cells to tackle variants of concern.

That appears to be the thinking of Quebec's director of public health, Dr. Horacio Arruda, who said on Thursday that there are stories of people developing even stronger immunity to the novel coronavirus when doses are mixed.

"I think that if you received the Pfizer one, you could receive, probably,Moderna," he said.

The protocol is to give two dosesof the same vaccine, Arruda said, but "if there is no available Pfizer and you have Moderna, I think the recommendation will be that you can change it."

WATCH | Dr. Horacio Arruda says mixing vaccines can boost immunity:

Quebec considers mixing vaccines for 2nd dose

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Dr. Horacio Arruda says mRNA vaccines could be swapped for follow up doses if shortages persist.

Studies still need to be done when it comes to mixing in AstraZeneca-Oxford, a viral vector vaccine, with an mRNA vaccine, Arrudasaid.But even in that scenario, people would develop a "good immunity."

Theinitial goal was to administer the second dose to residents in CHSLDs, the province's publiclyfunded long-term care institutions,around 112 days after the first.Already, about 130 days have elapsed since the vaccine campaign began on Dec. 14. Now, Quebec says the goal is to get those residentsvaccinated by May 8.

LTC homes in Montreal to administer Pfizer

Among those who will likely receive a different second vaccine are long-term care residents in Montreal's west end.

The CIUSSS du Centre-Sud-de-l'le-de-Montral will be giving residents the Pfizer vaccine starting Monday, according to Dr. Sophie Zhang, who oversees 15 long-term care centres.

"We do know that people who are older and have more illness tend to have a weaker response to the first dose," she said. "Given that, giving them a booster dose would be the best thing to do as quickly as possible."

Dr. Lisa Barrett, an infectious diseases physician and researcher at Dalhousie University in Halifax, said she doesn't see any reason to be worried about safety.

Barrett likens the first shot to giving your immune system an elementary school education. The second dose broadens the response to a university level.

"What your first shot does is it sends up a battle cry, if you will, to your immune system to rally those specific troops together to get an immune response that's good to this particular part of COVID vaccine and then it adds some memory," Barrett said.

"The quality of the immune response after one shot is generally OK, but still not highly sophisticated."

WATCH | What administering different types of COVID-19 vaccines could mean:

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A new trial is looking into the possibility of getting different types of COVID-19 vaccines for each dose and what it could mean for the fight against COVID-19.

Better to act now than wait: epidemiologist

With outbreaks hitting long-term care homes, it'sbetter to act now rather than wait, said Dr. Gaston De Serres of Quebec's public health institute (INSPQ).

"If you have a choice of being given the same product or delaying the second dose, then it's probably better to give the second product than waiting for the Moderna product," said De Serres, who is anepidemiologist.

"Right now, as imperfect as it seems, it's the most logical approach we can use to protect our most vulnerable."